conference program · 2009. 12. 23. · conference program thursday, june 11 morning 8:55 – 9:00...

Conference program

Thursday, June 11

Morning

8:55 – 9:00 Opening remarks

9:00 – 9:40 S.-C. Zhang Quantum spin Hall effect and topological insulators 19:40 – 10:20 Z.D. Kvon Two-dimensional semimetal and excitonic insulator in HgTe

quantum wells 210:20 – 11:00 J. Checkelsky Divergent resistance in high magnetic field and

thermoelectric effects in graphene 3

11:00 – 11:30 Coffee break

11:30 – 12:10 D.A. Abanin Charge 2e skyrmions in bilayer graphene 4

12:10 – 12:50 P.M. Ostrovsky Ballistic transport in disordered graphene 5

12:50 – 14:15 Lunch

Afternoon

14:15 – 14:55 M. Gershenson Towards realization of topological order in Josephson arrays 614:55 – 15:35 V. Manucharyan Fluxonium: coherent single Cooper pair circuit free of charge

offsets 7


16:00 – 16:40 A.V. Ustinov Ultra-fast microwave-free manipulation of a SQUID qubit 816:40 – 17:20 A. Fedorov Controlling quantum tunneling in the flux qubit 917:20 – 18:00 O. Buisson Quantum dynamics in a “Camelback” potential of a dc

SQUID 10

19:00 – 21:00 Welcome party

Friday, June 12

Morning

9:00 – 9:40 K. Ensslin Correlated electron detection and backaction in quantum dots 119:40 – 10:20 M.D. Lukin Quantum control of single spins and photons in diamond 12

10:20 – 11:00 A.V. Lebedev Many-particle state and electron noise in a quantum wire withlocalized Coulomb interaction 13


11:30 – 12:10 M.S. Foster Termination of typical wavefunction multifractal spectra at theAnderson MIT: Field theory description using the functionalrenormalization group 14

12:10 – 12:50 E. Bettelheim Conformal restriction in condensed matter physics 15

12:50 – 14:15 Lunch

Afternoon

14:15 – 14:55 Yu.V. Nazarov Least probable physics: large temperature fluctuations 1614:55 – 15:35 J.P. Pekola Experiments on the quantum of heat conductance 17


16:00 – 16:40 A.D. Mirlin Non-equilibrium Luttinger liquids 1816:40 – 17:20 A. Polkovnikov Adiabatic dynamics in closed systems, heat, entropy and laws

of thermodynamics 1917:20 – 18:00 I.S. Burmistrov Charge relaxation resistance in the Coulomb blockade problem 20

Poster session and discussions

Saturday, June 13

Morning

9:00 – 9:40 S.D. Ganichev All-electric fast detection of the Stokes parametersof infrared and terahertz radiation 21

9:40 – 10:20 A. Koshelev Terahertz radiation from intrinsic Josephson junctionssynchronized by internal cavity resonance 22

10:20 – 11:00 V. Murav’ev Plasmonics: Science and terahertz applications 23


11:30 – 12:10 G. Scalari THz and sub-THz quantum cascade lasers 2412:10 – 12:50 T. Schapers Electron interference and flux quantization effects

in semiconductor nanowires 25

12:50 – 14:15 Lunch

Afternoon

Excursion and free time

Sunday, June 14

Morning

9:00 – 9:40 A. Buzdin Magnetic moment manipulation by a Josephson current 269:40 – 10:20 S.M. Frolov Ballistic spin resonance 27

10:20 – 11:00 I.A. Garifullin Experimental observation of the spin-screening effectin superconductor/ferromagnet mesoscopic structures by NMR 28


11:30 – 12:10 L.R. Tagirov Extinction and recovery of superconductivity by interferencein Nb/CuNi bilayers 29

12:10 – 12:50 V.V. Ryazanov Arrays and circuits with SFS π-junctions. Inverse andπ-periodical Josephson current-phase relations 30

12:50 – 14:15 Lunch

Afternoon

14:15 – 14:55 A.M. Finkel’stein Quantum kinetic approach for studying thermal transport:calculation of the Nernst effect 31

14:55 – 15:35 L. Faoro On the microscopic origin of excess low frequency flux1/f noise in qubits and SQUIDs 32


16:00 – 16:40 M.V. Feigelman Pseudogaped superconductivity near mobility edge 3316:40 – 17:20 L.B. Ioffe Superconductor-insulator transition in strongly disordered

superconductors 3417:20 – 18:00 G.B. Lesovik Quantum divisibility test and its application in mesoscopic

physics 35

Monday, June 15

Morning

9:00 – 9:40 A. Yacoby Broken symmetry and quantum hall ferromagnetismin suspended bilayer graphene 36

9:40 – 10:20 K.S. Novoselov Graphene and its chemical derivatives 3710:20 – 11:00 V. Bouchiat Graphene as an open platform for tuning 2D phase transitions 38


11:30 – 12:10 P. Hakonen Shot noise in graphene Josephson junctions 3912:10 – 12:50 M.Z. Hasan Direct detection of topological order in topological

insulators via imaging of spin-textured edge-states 4012:50 – 14:15 Lunch

Afternoon

14:15 – 14:55 H. Bouchiat High frequency dynamics of the superconducting phase in longSNS diffusive Josephson junctions coupled to a superconductingresonator 41

14:55 – 15:35 H. Courtois Thermal effects in hybrid superconducting nanostructures 42


16:00 – 16:40 F. Giazotto Out-of-equilibrium Josephson effect in Al/AlOx/Tiand V/AlOx/Al superconducting tunnel nanostructures 43

16:40 – 17:20 K. Arutyunov Relaxation of non-equilibrium quasiparticles in a superconductorat ultra-low temperatures 44

17:20 – 18:00 K.S. Tikhonov Nonstationary Josephson effects in SINIS junction 45

19:00 Conference dinner (evening wood party)

Tuesday, June 16

Morning

9:00 – 9:40 O. Astafiev Scattering of electromagnetic waves on a single artificial atom 469:40 – 10:20 P.J. Leek Coupling superconducting qubits using sideband transitions

in circuit QED 4710:20 – 11:00 J. Bylander Microwave interferometry with a superconducting artificial atom 48


11:30 – 12:10 A.N. Korotkov Non-projective measurement of solid-state qubits: theory andexperiments 49

12:10 – 12:50 E. Ilichev Weak continuous measurements of multiqubits systems 5012.50 – 13:30 Yu. Makhlin Period-doubling quantum detector 51

13:30 – 13:35 Conference closing

13:35 – 15.00 Lunch

Thursday, June 11, morning

Quantum spin Hall effect and topological insulators

S.-C. ZhangDept of Physics, Stanford University, CA 94305

Search for topologically non-trivial states of matter has become a important goal for condensed matter physics.Recently, a new class of topological insulators has been proposed. These topological insulators have an insulatinggap in the bulk, but have topologically protected edge states due to the time reversal symmetry. In two dimensionsthe edge states give rise to the quantum spin Hall (QSH) effect, in the absence of any external magnetic field. Ishall review the theoretical prediction of the QSH state in HgTe/CdTe semiconductor quantum wells, and its recentexperimental observation. The QSH effect can be generalized to three dimensions as the topological magneto-electriceffect (TME) of the topological insulators. I shall also present realistic experimental proposals to observe fractionalcharge, spin-charge separation and the deconfinement of the magnetic monopoles in these novel topological states ofmatter.

1


Two-dimensional semimetal and excitonic insulator in HgTe quantum wells

Z.D. Kvon, E.B. Olshanetsky, D.A. Kozlov, and N.N. MikhailovInstitute of Semiconductor Physics, Novosibirsk, Russia

The talk is devoted to the properties of 2D semimetal recently discovered in undoped HgTe quantum wells (QWs)with surfaces of the reduced symmetry. This semimetal results from size quantization in (013) and (112) surfaceoriented QWs with the inverted band structure having the thickness 18−21 nm. The value of the overlapping is about10 meV. So we have a true 2D semimetal similar to that of classical 3D semimetals such as Bi and Sb. The systemindicated gives the opportunity to get 2D semimetal with any ratio of the densities of two-dimensional electrons(Ns) and holes (Ps) by means of applying of the gate voltage. So a lot of new interesting transport propertiescaused by their simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positivemagnetoresistance; 2) electron mobility jump due to hole screening of electron scattering by impurities; 3) anomaloustemperature dependence of 2D semimetal resistance because of electron scattering by heavy holes. It is likely thiseffect is the first clear demonstration of the direct influence of a particle-particle inelastic Landau scattering on metalresistance. The excitonic insulator (EI) state induced by magnetic field is found. It exists between electron-like andhole-like quantum Hall liquid states at the point Ns = Ps and near it. It is shown that the transition semimetal–EI issimilar to normal metal–superconductor transition and corresponds to BCS-scenario: up to the critical temperatureTc ≈ 1 K no temperature dependence of the transport and capacitance response of the system is observed but justbelow Tc the strong insulator behavior characterizing by the gap of few K appears.

2


Divergent resistance in high magnetic field and mhermoelectric effects in graphene

J. Checkelsky, L. Li, and N.P. OngDepartment of Physics, Princeton University, Princeton, New Jersey 08544, USA

We have investigated the behavior of the resistance of graphene at the n = 0 Landau Level in an intense magneticfield H . Employing a low-dissipation technique (with power P < 3 fW), we find that, at low temperature T , theresistance at the Dirac point R0(H) undergoes a 1000-fold increase from ∼ 10 kΩ to 40 MΩ within a narrow intervalof field. The abruptness of the increase suggests that a transition to an insulating, ordered state occurs at the criticalfield Hc. Results from 5 samples show that Hc depends systematically on the disorder, as measured by the offsetgate voltage V0. Samples with small V0 display a smaller critical field Hc. Empirically, the steep increase in R0 fitsaccurately a Kosterlitz-Thouless-type correlation length over 3 decades. The curves of R0 vs. T at fixed H approachthe thermal-activation form with a gap ∆ ∼ 15 K as H → H−

c , consistent with a field-induced insulating state.Next, we report measurements of the thermopower S and Nernst signal Syx in graphene in a magnetic field H .

Both quantities show strong quantum oscillations vs. the gate voltage Vg. Our measurements for Landau Levelsof index n 6= 0 are in quantitative agreement with the edge-current model of Girvin and Jonson [1]. The inferredoff-diagonal thermoelectric conductivity αyx comes close to the quantum of Amps per Kelvin. At the Dirac point(n = 0), however, the width of the peak in αyx is very narrow. We discuss features of the thermoelectric response atthe Dirac point including the enhanced Nernst signal.

[1] S.M. Girvin and M. Jonson, J. Phys. C: Solid State Phys. 15, L1147 (1982).

3


Charge 2e skyrmions in bilayer graphene

D.A. AbaninPrinceton Center for Theoretical Science, Princeton University, Princeton, New Jersey 08544 and

Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106

S.A. Parameswaran and S.L. SondhiDepartment of Physics, Princeton University, Princeton, New Jersey 08544

Quantum Hall states that result from interaction induced lifting of the eight-fold degeneracy of the zeroth Landaulevel in bilayer graphene are considered. We show that at even filling factors electric charge is injected into the systemin the form of charge 2e skyrmions. This is a rare example of binding of charges in a system with purely repulsiveinteractions. We calculate the skyrmion energy and size as a function of the effective Zeeman interaction, and discusssignatures of the charge 2e skyrmions in the scanning probe experiments. For details, see Ref. [1].

[1] D.A. Abanin, S.A. Parameswaran, and S.L. Sondhi, arXiv:0904.0040 (2009).

4


Ballistic transport in disordered graphene

A. SchuesslerInstitut fr Nanotechnologie, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany

P.M. OstrovskyInstitut fr Nanotechnologie, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany and

L.D. Landau Institute for Theoretical Physics, RAS, 119334 Moscow, Russia

I.V. GornyiInstitut fr Nanotechnologie, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany and

A.F. Ioffe Physico-Technical Institute, 194021 Saint Petersburg, Russia

A.D. MirlinInstitut fr Nanotechnologie, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany

Inst. fur Theorie der kondensierten Materie, Universitat Karlsruhe, 76128 Karlsruhe, Germany andPetersburg Nuclear Physics Institute, 188300 Saint Petersburg, Russia

An analytic theory of ballistic electron transport in disordered graphene in “short-and-wide” geometry is developed.We consider a sample of a large width and analyze the evolution of the conductance, the shot noise, and the fullstatistics of the charge transfer with increasing length at the Dirac point. We apply a special technique similar to theKeldysh Green function formalism. Both limits of weak Gaussian disorder and rare strong impurities are considered.The disorder perturbation theory is further combined with the renormalization group approach. We calculate disordercorrections to the full counting statistics of the sample both in ballistic and diffusive regimes and discuss the crossoverbetween them. The universality of electron transport at the Dirac point is also discussed. Our analytic results are ina good agreement with the available numerical simulations of disordered graphene samples.

[1] A. Schuessler, P.M. Ostrovsky, I.V. Gornyi, and A.D. Mirlin, Phys. Rev. B 79, 075405 (2009).

5

June 11, Thursday, afternoon

Towards realization of topological order in Josephson arrays

M. GershensonDepartment of Physics and Astronomy, Rutgers University,

136 Frelinghuysen Rd., Piscataway, NJ 08854, USA

Recently it was predicted (see, e.g., [1–3]) that the arrays of small Josephson junctions with nontrivial topology mayexhibit a novel phase which is characterized by long-range order of pairs of Cooper pairs in the absence of long-rangecorrelations in single-Cooper-pair condensate. Experimental realization of this novel phase can facilitate the fabricationof fault-tolerant superconducting qubits exponentially protected from local noises [1, 3, 4]. Our experiments [5] withsmall Josephson arrays show that, indeed, the condensate of pairs of Cooper pairs can be observed in the absence ofcoherence in the single-Cooper-pair condensate. The charge transport in this regime is due to coherent co-tunnelingof pairs of Copper pairs, objects with charge 4e. These experiments suggest that even a relatively small prototypedevice is well protected against magnetic flux variations.

[1] L.B. Ioffe and M.V. Feigel’man, Phys. Rev. B 66, 224503 (2002).[2] B. Doucot and J. Vidal, Phys. Rev. Lett. 88, 227005 (2002).[3] B. Doucot et al., Phys. Rev. Lett. 90, 107003 (2003).[4] B. Doucot et al., Phys. Rev. B 71, 024505 (2005).[5] S. Gladchenko, D. Olaya, E. Dupont-Ferrier, B. Doucot, L.B. Ioffe, and M.E. Gershenson, Nature Physics 5, 48 (2009).

6


Fluxonium qubit: coherent, single Cooper pair circuit free of charge offsets

V. Manucharyan, J. Koch, L. Glazman, and M. DevoretYale University, Departments of Physics and Applied Physics, New Haven, CT, USA

Coulomb blockade effects in mesoscopic physics so far have always been observed in conjunction with the noiseof random charge “offsets”, inherent to many solid-state systems. In the case of superconducting tunnel junctiondevices, such charge“offsets” severely limit the promise of single Cooper pair quantum circuits for metrology andquantum information applications. We present a novel superconducting artificial atom, the Fluxonium, based on anarray of Josephson junctions. Its energy spectrum manifests the anharmonicity associated with single Cooper paireffects combined with total insensitivity to offset charges.

Fluxonium circuit consists of a small capacitance Josephson tunnel junction shunted by an array of larger junc-tions to form a loop. External magnetic field tunes the device. The junction parameters are chosen such that theresulting charge fluctuation across the small junction is approximately “1 e” while its conjugate phase fluctuation isapproximately “1 rad”. At the same time phase fluctuation across every array junction is much less than“1 rad”, sothat the offset charges on all circuit islands are screened. Such regime, unaccessible to conventional charge/phase/fluxqubits, makes Fluxonium transitions modestly dependent on the device parameters and flux bias (compared to fluxqubit) while staying strongly anharmonic (compared to phase and transmon qubits). At integer half flux quantumfrustrations the spectrum forms the 3-level “Λ”-system, particularly promising for long coherence and high fidelityquantum information manipulation.

The junction loop is capacitively coupled to a microwave transmission line resonator in order to perform a circuit-QED style dispersive readout of the qubit state. Despite the fact that the device consists of total of 44 junctions, thedecoherence time exceeds one microsecond (decoherence quality factor 105).

7


Ultra-fast microwave-free manipulation of a SQUID qubit

A.V. UstinovPhysikalisches Institut, Universitaet Karlsruhe, Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe, Germany

I will report on experiments with a tunable SQUID qubit manipulated without using microwaves, just by fewnanoseconds long pulses of magnetic flux [1]. We observe coherent oscillations of the occupation probabilities of twopersistent current states at a frequency tunable by the amplitude of the flux pulse within the range between 6 GHzand 21 GHz. The oscillations occur between the two lowest energy states of a single-well potential formed in theSQUID by the flux pulse. The oscillation frequency dependence on the control pulse amplitude is relatively weak, incontrast to the exponential sensitivity of the oscillation frequency in a double well potential. An advantage of thereported qubit operation is its relative immunity to both thermal and magnetic field fluctuations. The demonstratedoperation mode could allow for quantum gates faster than 100 ps, which is much shorter than gate times currentlyattainable in other superconducting qubits.

[1] S. Poletto, F. Chiarello, M.G. Castellano, J. Lisenfeld, A. Lukashenko, C. Cosmelli, G. Torrioli, P. Carelli, and A.V. Ustinov,New J. Phys. 11, 013009 (2009).

8


Controlling quantum tunneling in the flux qubit

A. Fedorov, F.G. Paauw, C.J.P.M Harmans, and J.E. MooijKavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft

Recent advances in experiments with a flux qubit include demonstration of single and two qubit quantum gates aswell as a coupling between the flux qubit and a harmonic oscillator. In all experiments the best coherence propertiesof the flux qubit have been achieved at qubit’s degeneracy point where the energy level splitting is minimal (gap) anddetermined solely by quantum tunnelling in a double-well potential. However, since the potential barrier and the gapof the conventional flux qubit are fully fixed by fabrication, one needs to tune the qubit out of the degeneracy point inorder to bring it in resonance with another quantum system. We overcame this limitation by means of an additionalflux loop and experimentally demonstrated the in situ tunability of the gap of a superconducting flux qubit [1]. Pulsesapplied via a local control line allowed us to tune the gap over a range of several GHz on a nanosecond timescale.The strong flux sensitivity of the gap opens up the possibility to create new control schemes and different types oftunable couplings that are effective at the degeneracy point of the qubit. Relaxation time of the qubit as function ofthe potential barrier height was also investigated

[1] F.G. Paauw, A. Fedorov, C.J. Harmans, and J.E. Mooij, Phys. Rev. Lett. 102, 090501 (2009).

9


Quantum dynamics in a “Camelback” potential of a dc SQUID

E. Hoskinson, F. Lecocq, N. Didier, A. Fay, Z. Peng, F.W. Hekking, W. Guichard, and O. BuissonInsitut Neel and LPMMC, CNRS/UJF, 25 Avenue des Martyrs, BP 166, 38042, Grenoble, France

R. Dolata, B. Mackrodt, and A.B. ZorinPTB, Bundesallee 100, 38116 Braunschweig, Germany

We investigate a quadratic-quartic anharmonic quantum oscillator formed by a potential well between two potentialbarriers, called “Camelback” potential. This novel potential shape has been realized with a dc SQUID at near-zerocurrent bias and flux bias near half a flux quantum. Escape out of the central well can occur via tunneling througheither of the two barriers. Escape measurements are well explained with a generalized double-path macroscopic quan-tum tunneling theory. We also demonstrate phase qubit properties in this quadratic-quartic “Camelbac” potential.We perform a nanosecond single shot measurement by applying a flux pulse which reduces the height of the twopotential barriers, allowing the excited state of the qubit to escape by two independent paths to an adjacent fluxstate of the dc-SQUID. We find Rabi oscillation, Ramsey oscillation, and energy relaxation decay times on the orderof 60 ns, 20 ns, and 100 ns, respectively. Via spectroscopy, we also demonstrate an “optimal line” in current and fluxbias along which the phase qubit is insensitive to decoherence due to low-frequency current fluctuations.

This work was supported by the EU project EuroSQIP.

10

Friday, June 12, morning

Correlated electron detection and backaction in quantum dots

B. Kung, S. Gustavsson, U. Gasser, I. Shorubalko, T. Choi, R. Leturcq, T. Ihn, and K. EnsslinSolid State Physics, ETH Zurich, 8093 Zurich, Switzerland

Quantum dots with best quality for transport experiments are usually realized in n-type AlGaAs/GaAs heterostruc-tures. Novel material systems, such as graphene, nanowires and p-type heterostructures offer unexplored parameterregimes in view of spin-orbit interactions, carrier-carrier interactions and hyperfine coupling between electron andnuclear spins, which might be relevant for future spin qubits realized in quantum dots. With more sophisticated nan-otechnology it has become possible to fabricate coupled quantum systems where classical and quantum mechanicalcoupling and back action is experimentally investigated. By using a quantum point contact as a charge read-outfor a nearby capacitively coupled quantum dot the time-resolved transport of individual electrons can be monitored[1]. This has been extended to study super-Poisonian noise [2] and higher-order noise correlations [3] as well assingle-photon detection [4] by a double dot and time-resolved single-electron interference [5]. Using InAs nanowirequantum dots placed on top of a quantum point contact in an AlGaAs heterostructure [6] leads to a stronger couplingof the two systems and allows to compare charge counting with conventional current measurements [7], to extendthe detector bandwidth to the THz regime [8] and to investigate cotunneling events [9]. Also the backaction due tophonons [10] was investigated. The use of two quantum point contact detectors allowed to study correlated counting[11] and cross-correlation techniques [12].

[1] S. Gustavsson, R. Leturcq, B. Simovic, R. Schleser, T. Ihn, P. Studerus, K. Ensslin, D.C. Driscoll, and A.C. Gossard,Phys. Rev. Lett. 96, 076605 (2006).

[2] S. Gustavsson, R. Leturcq, B. Simovic, R. Schleser, P. Studerus, T. Ihn, K. Ensslin, D.C. Driscoll, and A.C. Gossard,Phys. Rev. B 74, 195305 (2006).

[3] S. Gustavsson, R. Leturcq, T. Ihn, K. Ensslin, M. Reinwald, and W. Wegscheider, Phys. Rev. B 75, 075314 (2007).[4] S. Gustavsson, M. Studer, R. Leturcq, T. Ihn, K. Ensslin, D.C. Driscoll, and A.C. Gossard, Phys. Rev. Lett. 99, 206804

(2007).[5] S. Gustavsson, R. Leturcq, M. Studer, T. Ihn, K. Ensslin, D.C. Driscoll, and A.C. Gossard, Nanoletters 8, 2547 (2008).[6] I. Shorubalko, R. Leturcq, A. Pfund, D. Tyndall, R. Krischek, S. Schon, and K. Ensslin, Nanoletters 8, 382 (2008).[7] S. Gustavsson, I. Shorubalko, R. Leturcq, S. Schon, and K. Ensslin, Appl. Phys. Lett. 92, 152101 (2008).[8] S. Gustavsson, I. Shorubalko, R. Leturcq, T. Ihn, K. Ensslin, and S. Schon, Phys. Rev. B 78, 035324 (2008).[9] S. Gustavsson, M. Studer, R. Leturcq, T. Ihn, K. Ensslin, D.C. Driscoll, and A.C. Gossard, Phys. Rev. B 78, 155309 (2008).[10] U. Gasser, S. Gustavsson, B. Kung, K. Ensslin, T. Ihn, D.C. Driscoll, and A.C. Gossard, Phys. Rev. B 79, 035303 (2009).[11] T. Choi, I. Shorubalko, S. Gustavsson, S. Schon, and K. Ensslin, N. J. Phys. 11, 013005 (2009).[12] B. Kung, O. Pfaffli, S. Gustavsson, T. Ihn, K. Ensslin, M. Reinwald, and W. Wegscheider, Phys. Rev. B 79, 035314 (2009).

11


Quantum control of single spins and photons in diamond

M.D. LukinHarvard-MIT Center for Ultracold Atoms, Department of Physics,

Harvard University, Cambridge, Massachusetts 02138, USA

In this talk we will discuss recent developments involving quantum manipulation of individual spins and photonsusing Nitrogen Vacancy impurities in diamond and sub-wavelength optical localization techniques. Novel applicationsincluding realization of distributed quantum information systems and nanoscale magnetic sensing will be discussed.

12


Many-particle state and electron noise in a quantum wire with localized Coulombinteraction

A.V. LebedevL.D. Landau Institute for Theoretical Physics, RAS, 119334 Moscow, Russia and

Theoretische Physik, Schafmattstrasse 32, ETH-Zurich, CH-8093 Zurich, Switzerland

G. BlatterTheoretische Physik, Schafmattstrasse 32, ETH-Zurich, CH-8093 Zurich, Switzerland

We consider a ballistic one-dimensional conductor including Coulomb interaction in a finite region of the conductordescribed within a capacitive approximation. Following our previous work [1], we assume that all effects of interactioncan be incorporated into a mutual phase accumulated by the electrons during the propagation through the interactingregion. This assumption holds true for a Coulomb energy much smaller then the Fermi energy of the conductor. Itthen is possible to construct the many-particle scattering state in a non-stationary situation where a finite voltagebias is applied to the system. We make use of this state to calculate the one-particle occupation numbers and showthat as a function of energy it exhibits a Fermi liquid type discontinuity at the Fermi level. We suggest an electronnoise measurement to detect this feature in a realistic setup.

[1] A.V. Lebedev, G.B. Lesovik, and G. Blatter, Phys. Rev. Lett. 100, 226805 (2008).

13


Termination of typical wavefunction multifractal spectra at the Anderson MIT: Fieldtheory description using the functional renormalization group

M.S. FosterDepartment of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA

S. RyuDepartment of Physics, University of California, Berkeley, CA 94720, USA

A.W.W. LudwigDepartment of Physics, University of California, Santa Barbara, CA 93106, USA

We revisit the problem of wavefunction statistics at the Anderson metal-insulator transition (MIT) of non-interactingelectrons in d > 2 spatial dimensions. At the transition, the complex spatial structure of the critical wavefunctionsis reflected in the non-linear behavior of the multifractal spectrum of generalized inverse participation ratios (IPRs).Beyond the crossover from narrow to broad IPR statistics, which always occurs for sufficiently large moments of thewavefunction amplitude, the spectrum obtained from a typical wavefunction associated with a particular disorderrealization differs markedly from that obtained from the disorder-averaged IPRs. This phenomenon is known as thetermination of the multifractal spectrum. We provide a field theoretical derivation for the termination of the typicalmultifractal spectrum, by combining the non-linear sigma model framework, conventionally used to access the MITin d = 2 + ǫ dimensions, with a functional renormalization group (FRG) technique. The FRG method deployed herewas originally pioneered to study the properties of the two-dimensional (2D) random phase XY model [1]. The samemethod was used to demonstrate the termination of the multifractal spectrum in the very special problem of 2D Diracfermions subject to a random Abelian vector potential. Our result shows that the typical multifractal wavefunctionspectrum and its termination can be obtained at a generic Anderson localization transition in d > 2, within thestandard field theoretical framework of the non-linear sigma model, when combined with the FRG.

[1] D. Carpentier and P. Le Doussal, Nucl. Phys. B 588, 565 (2000).

14


Conformal restriction in condensed matter physics

E. BettelheimRacah Institute of Physics, Hebrew University of Jerusalem

Conformal restriction theory allows one to describe two dimensional models at criticality which possess conformalsymmetry and have vanishing central charge. The theory, developed by probabilists, describes completely the geometryof certain clusters in such systems. I will discuss in particular how the theory can be applied to the integer quantumHall transition making use of the Chalker-Conddington model.

15

Friday, June 12, afternoon

Least probable physics: large temperature fluctuations

Yu.V. NazarovKavli Institute of NanoScience, Delft University of Technology, 2628 CJ Delft, The Netherlands

T.T. HeikkilaLow Temperature Laboratory, Helsinki University of Technology, P.O. Box 5100 FIN-02015 TKK, Finland

We study the statistics of the fluctuating electron temperature in a metallic island coupled to reservoirs via resistivecontacts and driven out of equilibrium by either a temperature or voltage difference between the reservoirs. Thefluctuations of temperature are well-defined provided that the energy relaxation rate inside the island exceeds therate of energy exchange with the reservoirs. We quantify these fluctuations in the regime beyond the Gaussianapproximation and elucidate their dependence on the nature of the electronic contacts.

It turns out that large fluctuations are described by equations that give the least probable evolution of a non-lineardissipative system. This is in a sharp contrast with a common point of view that physics and physical laws areapplicable to most probable course of events only and cannot describe wonders. We argue that this is not so andshow that the laws of the least probable physics are not less deterministic than the laws of the most probable one.

[1] T.T. Heikkila and Yu.V. Nazarov, Phys. Rev. Lett. 102, 130605 (2009).

16


Experiments on the quantum of heat conductance

J.P. Pekola, M. Meschke, A.V. Timofeev, and M. HelleLow Temperature Laboratory, Helsinki University of Technology, P.O. Box 3500, 02015 TKK, Finland

W. GuichardInstitut Neel, C.N.R.S.- Universite Joseph Fourier, BP 166, 38042 Grenoble-cedex 9, France

M. MottonenLow Temperature Laboratory, Helsinki University of Technology, P.O. Box 3500, 02015 TKK, Finland and

Department of Applied Physics/COMP, Helsinki University of Technology P. O. Box 5100, 02015 TKK, Finland

The fundamental limit to transmit heat via a single channel is governed by the quantum of thermal conductance.This has been demonstrated in experiments on both phonons [1, 2] and electrons [3]. Here we present two exper-iments [4, 5] on this phenomenon based on electromagnetic coupling (photons). In the first experiment tunableelectric impedance is used to modulate the radiated heat between two resistors at different temperatures in a su-perconducting micro-circuit. In the second experiment we demonstrate electronic refrigeration at the quantum limitusing superconductor-normal metal tunnel junctions. We discuss the limits of classical and quantum heat exchangein an electrical circuit, and the crossover between quasiparticle and photonic heat conduction.

[1] K. Schwab, E.A. Henriksen, J.M. Worlock, and M.L. Roukes, Nature 404, 974 (2000).[2] C.S. Yung, D.R. Schmidt, and A.N. Cleland, Appl. Phys. Lett. 81, 31 (2002).[3] O. Chiatti, J.T. Nicholls, Y.Y. Proskuryakov, N. Lumpkin, I. Farrer, and D.A. Ritchie, Phys. Rev. Lett. 97, 056601 (2006).[4] M. Meschke, W. Guichard, and J.P. Pekola, Nature 444, 187 (2006).[5] A.V. Timofeev, M. Helle, M. Meschke, M. Mottonen, and J.P. Pekola, Phys. Rev. Lett. 102, 200801 (2009).

17


Non-equilibrium Luttinger liquids

A.D. MirlinInstitut fur Nanotechnologie, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany

Institut fur Theorie der kondensierten Materie, Universitat Karlsruhe, 76128 Karlsruhe, Germany andPetersburg Nuclear Physics Institute, 188300 St. Petersburg, Russia

D.B. GutmanInstitut fur Theorie der kondensierten Materie, Universitat Karlsruhe, 76128 Karlsruhe, Germany

Y. GefenDept. of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel

We develop [1–3] the bosonization formalism for Luttinger liquids out of equilibrium. It allows us to build atheory of tunneling spectroscopy of interacting electrons in a nonequilibrium quantum wire coupled to reservoirs. Theproblem is modeled as a Luttinger liquid structure with spatially dependent interaction and with non-equilibrium(in general, different) energy distributions of left- and right-movers. The interaction leads to the renormalizationof the tunneling density of states, as well as to the redistribution function of electrons over energies. The energyrelaxation is controlled by the plasmon scattering on the boundary between regions with different interaction strengthand affects the distribution function of electrons in the wire as well as of those emitted from the interacting regionsinto electrodes. We further calculate the dephasing which governs the smearing of zerobias anomalies in the tunnelingdensity of states.

Our general result for the non-equilibrium electron Green function is expressed in terms of functional determinantsrelated (via an analytical continuation) to those arising in the problem of electron counting statistics. The resultshows an intrinsic relation of the dephasing and energy redistribution physics in the Luttinger-liquid structures to“fractionalization” of electron-hole excitations (phase pulses) in the tunneling process and at boundaries with non-interacting leads.

[1] D.B. Gutman, Y. Gefen, and A.D. Mirlin, Phys. Rev. Lett. 101, 126802 (2008).[2] D.B. Gutman, Y. Gefen, and A.D. Mirlin, arXiv:0903.3333 (2009).[3] D.B. Gutman, Y. Gefen, and A.D. Mirlin, to be published.

18


Adiabatic dynamics in closed systems, heat, entropy and laws of thermodynamics

A. PolkovnikovBoston University

In this talk I will first discuss the connection between quantum and thermodynamic adiabatic theorems and willsuggest there are three generic regimes of response of closed many-body systems to slow external perturbations. Iwill argue that in all three regimes thermodynamic adiabatic theorem follows from the quantum adiabatic theorem.I will illustrate these regimes using several examples including sweeps through a quantum critical point. Based onthis connection I will introduce microscopic expressions for the heat and diagonal entropy and will show that theirbehavior is consistent with the first and the second laws of thermodynamics.

19


Charge relaxation resistance in the Coulomb blockade problem

Ya.I. Rodionov, I.S. Burmistrov, and A.S. IoselevichL.D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, 117940 Moscow, Russia

We study the dissipation in a system consisting of a small metallic island coupled to a gate electrode and to a massivereservoir via single tunneling junction. The dissipation of energy is caused by a slowly oscillating gate voltage. Wecompute it in the regimes of weak and strong Coulomb blockade. We focus on the regime of not very low temperatureswhen electron coherence can be neglected but quantum fluctuations of charge are strong due to Coulomb interaction.The answers assume a particularly transparent form while expressed in terms of specially chosen physical observables:charge relaxation resistance amd the observable recently introduced in Ref. [1]. We discovered that the dissipationrate is given by a universal expression in both limiting cases [2].

[1] I.S. Burmistrov and A.M.M. Pruisken, Phys. Rev. Lett. 101, 056801 (2008); I.S. Burmistrov and A.M.M. Pruisken, AIPConference Proceedings 1134, 101 (2009).

[2] Ya.I. Rodionov, I.S. Burmistrov, and A.I. Ioselevich, arXiv:0905.2688 (2009), to be published.

20

Saturday, June 13, morning

All-electric fast detection of the Stokes parameters of infrared and terahertz radiation

S.D. GanichevPhysics Department, University of Regensburg, 93040 Regensburg, Germany

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with abandwidth that stretches from the infrared to the terahertz range [1,2]. The device consists of two elements, onein front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elementsrespectively utilise the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effectin a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, andfor the latter, bulk GaAs. In contrast with optical methods our device is an easy to handle all-electric approach,which we demonstrated by applying a large number of different lasers from low power, continuous wave systems tohigh power, pulsed sources.

[1] S.D. Ganichev, W. Weber, J. Kiermaier, S.N. Danilov, D. Schuh, W. Wegscheider, Ch. Gerl, D. Bougeard, G. Abstreiter,and W. Prettl, J. Appl. Physics 103, 114504 (2008).

[2] S.N. Danilov, B. Wittmann, P. Olbrich, W. Eder, W. Prettl, L.E. Golub, E.V. Beregulin, Z.D. Kvon, N.N. Mikhailov,S.A. Dvoretsky, V.A. Shalygin, N.Q. Vinh, A.F.G. van der Meer, B. Murdin, and S.D. Ganichev, J. Appl. Physics 105,013106 (2009).

21


Terahertz radiation from intrinsic Josephson junctions synchronized by internal cavityresonance

A. Koshelev, U. Welp, C. Kurter, K.E. Gray, and W.-K. KwokMaterials Science Division, Argonne National Laboratory,USA

L. BulaevskiiLos Alamos National Laboratory, USA

L. OzyuzerDepartment of Physics, Izmir Institute of Technology, Turkey

K. Kadowaki, T. Yamamoto, H. Minami, and H. YamaguchiInstitute of Materials Science, University of Tsukuba, Japan

Intrinsic Josephson-junction stacks are realized in mesas fabricated out of high-temperature superconductors. Theymay generate powerful and coherent electromagnetic radiation in terahertz range provided Josephson oscillations aresynchronized in all junctions in the stack. A promising way to facilitate such synchronization is to excite the in-phaseFiske mode with the frequency set by stack lateral size [1, 2]. Resonant continuous-wave radiation with powers upto several microwatts has been extracted from mesoscopic crystals of the layered high-temperature superconductorBi2Sr2CaCu2O8 [1]. The observed resonance frequencies are in the range 0.4−0.85 THz, they do not depend on tem-perature and scale roughly inversely proportional to the mesa widths, consistent with the Fiske-resonance mechanism.

The mechanism of energy pumping into this mode in zero magnetic field is a nontrivial issue. Josephson oscillationsidentical in all junctions are directly coupled to Fiske modes only in mesas with lateral modulation of the Josephsoncritical current [2]. New inhomogeneous dynamic state providing such coupling has been demonstrated recently [3]. Inthis state the phase-oscillation patterns are different in odd and even junctions in the stack. The phase shift betweenthe oscillations in neighboring junctions is static and varies from 0 to 2π in a narrow region near the stack center(phase kink). The oscillating electric and magnetic fields are almost homogeneous in all the junctions. The formationof this state promotes efficient pumping of the energy into the cavity resonance. We will also discuss several relevantissues including (i) limits of the radiation power and power-conversion efficiency, (ii) mechanisms of damping of theresonance mode including radiations into free space and into the base crystal, (iii) stability of coherent states, and(iv) synchronization in inhomogeneous mesas.

This work was supported by the U.S. DOE, Office of Science, under contract #DE-AC02-06CH11357.

[1] L. Ozyuzer et al., Science 318, 1291 (2007); K.E. Gray et al., arXiv:0901.4290 (2009).[2] A.E. Koshelev and L.N. Bulaevskii, Phys. Rev. B 77, 014530 (2008).[3] Sh. Lin and X. Hu, Phys. Rev. Lett., 100, 247006 (2008); A.E. Koshelev, Phys. Rev. B 78, 174509 (2008).

22


Plasmonics: science and terahertz applications

V. Muravev and I. KukushkinInstitute of Solid State Physics, RAS, Chernogolovka, 142432 Russia

There has been an increasing interest in the basic properties of robust collective phenomena such as plasma excita-tions in low-dimensional electron systems. Compared with, for example light waves, plasma excitations offer powerfuladditional degrees of freedom to alter the dispersion, since the plasmon velocity is easily tuned through the applicationof a magnetic field or by changing the electron density. For this reason different wave phenomena such as interferenceand tunable band gap formation could be investigated on a single semiconductor nanostructure [1]. The plasmonproperties are greatly affected by the dielectric properties of matter in the immediate vicinity of the two-dimensionalelectron system. This fact gives a convenient tool to manipulate with the plasmon dispersion low and gives rise toa whole series of unconventional plasma modes [2]. An important impetus to study plasma waves in nanostructurescomes from potential applications. The fact that resonant plasmon frequency falls into the terahertz frequency rangemake it possible to build a new generation of low-cost, tunable giga-terahertz on-chip detectors-spectrometers. Matrixcameras can be easily created on the basis of the single detector. The cameras may be used for terahertz vision [3].

[1] V.M. Muravev, A.A. Fortunatov, I.V. Kukushkin, J.H. Smet, W. Dietsche, and K. von Klitzing, Phys. Rev. Lett. 101,216801 (2008).

[2] V.M. Muravev, C. Jiang, I.V. Kukushkin, J.H. Smet, V. Umansky, and K. von Klitzing, Phys. Rev. B 75, 193307 (2007).[3] I.V. Kukushkin and V.M. Muravev, U.S. Patent Application “Apparatus and Method of Detecting Electromagnetic Radia-

tion” (2008).

23


THz and sub-THz quantum cascade lasers

G. Scalari, M.I. Amanti, J. Lloyd-Hughes, C. Walther, M. Fischer, R. Terazzi, M. Beck, and J. FaistInstitute of Quantum Electronics, ETH Zurich, Switzerland

H. Beere and D. RitchieCavendish Laboratory, University of Cambridge, Cambridge, UK

The quantum cascade (QC) laser [1] is a semiconductor laser based on intersubband transition in quantum wells.Nowadays, it covers a considerable portion of the electromagnetic spectrum, from 2.9 µm to more than 300 µm.

In this talk, we will review the recent progress and achievements in the realization and the study of QC lasersoperating in the THz range (1−5 THz) [2, 3]. Pulsed operating temperatures recently reached 186 K [4] and seemto follow the phenomenological relationship hν ≤ kBT [2]. We will present recent data on high performance THzQC lasers based on resonant phonon extraction showing low threshold current densities (100−200 A/cm2) and pulsedoperating temperatures up to 160 K. Our laboratory particularly focused on the realization of low frequency (below 2THz) THz QC lasers with two different approaches: lasers based on a bound-to-continuum transition [5] and structuresdesigned to exploit the additional confinement arising from an intense magnetic field applied perpendicularly to theplane of the quantum wells [3]. This condition of further confinement reduces substantially the intersubband scatteringrates and threshold current densities as low as 1 A/cm2 can be observed together with resonances in transport andlight emission that can be ascribed to many body processes [6]. The magnetic confinement reveals its efficiency alsofor the selective injection into narrowly spaced energy states: we demonstrated laser action at sub-THz frequencies(hν = 4 meV) [3] and new results demonstrating laser action on a spatially diagonal transition tunable from 730GHz to 1.39 THz will be presented. In presence of magnetic confinement, the optical phonon emission is stronglyquenched, allowing the observation of laser action for temperature values that overcome the empirical rule hν ≤ kBT[7]: we will present data of 1 THz laser emission up to 116 K for an applied field value of 7.3 T.

[1] J. Faist, F. Capasso, D. Sivco, C. Sirtori, A. Hutchinson, and A. Cho, Science 264, 553 (1994).[2] B.S. Williams, Nature Photonics 1, 517 (2007).[3] G. Scalari, C. Walther, M. Fischer, R. Terazzi, H. Beere, D. Ritchie, and J. Faist, Laser and Photonics Reviews 3, 45 (2009).[4] S. Kumar, Q. Hu, , and J.L. Reno, Appl. Phys. Lett. 94, 131105 (2009).[5] C. Walther, G. Scalari, J. Faist, H. Beere, and D. Ritchie, Appl. Phys. Lett. 89, 231121 (2006).[6] G. Scalari, S. Blaser, J. Faist, H. Beere, E. Linfield, D. Ritchie, and G. Davies, Phys. Rev. Lett. 93, 237403 (2004).[7] A. Wade, G. Fedorov, S. Kumar, B.S. Williams, Q. Hu, J.L. Reno, and D. Smirnov, Nature Photonics 3, 41 (2009).

24


Electron interference and flux quantization effects in semiconductor nanowires

T. SchapersInstitute of Bio- and Nanosystems (IBN 1), JARA — Fundamentals of Future

Information Technologies, Research Centre Julich, 52425 Julich, Germany

Semiconductor nanowires are versatile building blocks for the design of future electronic devices [1]. Among themany possible materials suitable for semiconductor nanowires, InN is particularly interesting because of its lowenergy band gap and its high surface conductivity [2]. At low temperatures electron interference effects often playan important role in the transport characteristics of nanostructures. The characteristic length connected to electroninterference is the phase-coherence length lφ, i.e. the length over which phase-coherent transport is maintained. Incase that the phase-coherence length is in the order of the device dimensions, interference effects can be employed toenhance the device functionality.

We studied the quantum transport in InN nanowires grown by plasma-assisted molecular beam epitaxy [2]. Themeasured wires had a diameter ranging from about 40 nm up to 130 nm and a length of approximately 1 µm. Aftergrowth the InN nanowires were dispersed on the patterned SiO2-covered Si substrate and contacted individually usingelectron beam lithography. The wires show a metal-type temperature dependence of the resistance. The presence ofa tubular surface electron gas is confirmed by the conductance scaling with the nanowire diameter. Information onthe phase-coherent transport is gained from the fluctuation pattern in the magnetoresistance. It is found that thefluctuation amplitude decreases substantially if the temperature is increased, which can be attributed to the enhancedphase-breaking at elevated temperatures. The phase-coherence length at different temperatures is determined fromthe average fluctuation amplitude as well as from the correlation field. At temperatures below 1 K we find thatphase-coherence is maintained in the complete wire structure [3].

For nanowires with a very small diameter below 40 nm pronounced flux periodic oscillations in the magneto-conductance are observed which can be attributed to the formation of coherent circular quantum states on in thetube-like surface electron gas [4].

Work done in collaboration with Sergio Estevez Hernandez, Christian Blomers, Thomas Richter, Karl Weis, GunnarPetersen, Robert Frielinghaus, Shima Algha, Christian Volk, Raffaella Calarco, Hans Luth (Julich), Michel Marso(University of Luxembourg), and Michael Indlekofer (Wiesbaden University of Applied Sciences).

[1] L. Samuelson et al., Phyisca E 25, 313 (2004); W. Lu and C.M. Lieber, J. Phys. D 39, R387 (2006).[2] R. Calarco and M. Marso, Appl. Phys. A 87, 499 (2007).[3] Ch. Blomers, Th. Schapers, T. Richter, R. Calarco, H. Lth, and M. Marso, Appl. Phys. Lett. 92, 132101 (2008).[4] T. Richter, Ch. Blomers, H. Luth, R. Calarco, M. Indlekofer, M. Marso, and Th. Schapers, Nano Lett. 8, 2834 (2008).

25

Sunday, June 14, morning

Magnetic moment manipulation by a Josephson current

A. BuzdinInstitut Universitaire de France and University Bordeaux I,

351 cours de la Liberation, 33405, Talence, France

Josephson junction where the weak link is formed by a noncentrosymmetric ferromagnet has very interestingproperties. The ground state of this junction is characterized by the finite phase difference ϕ0, which is proportionalto the strength of the spin-orbit interaction and the exchange field in the normal metal [1]. Such ϕ0-junction gives adirect coupling between the superconducting current and the magnetic moment. The superconducting current mayprovoke the flip of the magnetic moment and the ac Josephson effect generates a magnetic precession providing then afeedback to the current. Magnetic dynamics result in several anomalies of current-phase relations (second harmonic,dissipative current) which are strongly enhanced near the ferromagnetic resonance frequency [2]. The ϕ0-junctionsopen interesting perspectives for the superconducting spintronics.

[1] A. Buzdin, Phys. Rev. Lett. 101, 107005 (2008).[2] F. Konschelle and A. Buzdin, Phys. Rev. Lett. 102, 017001 (2009).

26


Ballistic spin resonance

S.M. FrolovKavli Institute of NanoScience, Delft University of Technology, 2628 CJ Delft, The Netherlands

We demonstrate spin resonance driven by ballistic motion of electrons and mediated by spin-orbit interaction in amicron-scale channel of GaAs/AlGaAs two-dimensional electron gas. The resonance is observed when the frequencyof electron bouncing trajectories in the channel matches the spin precession frequency set by a large in-plane magneticfield. The resonance is manifested as a suppression of pure spin currents that are generated in the channel by injectionthrough quantum point contacts. The resonant frequency (10−50 GHz) can be tuned by varying electron density orchannel width, as well as by bending the electron trajectories with a small out-of-plane magnetic field. Ballistic spinresonance can be used to determine the anisotropy in spin-orbit interaction, as well as a principle of operation of aspin field-effect transistor.

27


Experimental observation of the spin-screening effect in superconductor/ferromagnetmesoscopic structures by NMR

I.A. Garifullin, R.I. Salikhov, and N.N. Garif’yanovZavoisky Physical-Technical Institute, 420029 Kazan, Russia

L.R. TagirovKazan State University, 42008 Kazan, Russia

K. Westerholt and H. ZabelInstitut fur Experimentalphysik/Festkorperphysik, Ruhr-Universitat Bochum, D-44780 Bochum, Germany

We have performed the study of the so-called spin screening effect in thin film ferromag-net/superconductor/ferromagnet (F/S/F) heterostructures which we observed for the first time recently [1]using the nuclear magnetic resonance (NMR) technique. As an F-layer we used Pd1−xFex alloys or Ni, and as anS-layer V. We studied NMR of 51V nuclei in the normal and superconducting states for parallel and perpendicularorientation of the sample plane relative to the orientation of the external magnetic field. When studying NMR ofNi/V/Ni trilayers we obtained that qualitatively the distortion of the high-field wing of the resonance line which iscaused by the spin screening effect does not depend on the orientation of the sample relative to the direction of dcmagnetic field. We also found that the effect disappears with increasing V-layer thickness in complete agreementwith the theory by Bergeret et al. [2].

[1] R.I. Salikhov, I.A. Garifullin, L.R. Tagirov, K. Thes-Brohl, K. Westerholt, and H. Zabel, Phys. Rev. Lett. 102, 087003(2009).

[2] F.S. Bergeret, A.F. Volkov, and K.B. Efetov, Europhys. Lett. 66, 111 (2004); Phys. Rev. B 69, 174504 (2004).

28


Extinction and recovery of superconductivity by interference in Nb/CuNi bilayers

L.R. TagirovSolid State Physics Department, Kazan State University, Kazan, 420008, Russia

V. Zdravkov, R. Morari, and A. SidorenkoInstitute of Electronic Engineering and Industrial Technologies ASM, Kishinev, MD2028, Moldova

J. Kehrle, G. Obermeier, S. Gsell, M. Schreck, C. Muller, S. Horn, and R. TidecksInstitut fur Physik, Universitat Augsburg, Augsburg, D-86159, Germany

V.V. RyazanovInstitute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, 142432, Russia

In superconductor-ferromagnetic metal (S/F) contacts the superconducting condensate penetrates through the S/Finterface into an F-layer, and the pairing wave function not only decays into the F metal, but simultaneously oscillates.Based on this oscillating pairing function a variety of new physical effects were predicted (see reviews [1] and referencestherein). Some of them were observed experimentally: a non-monotonous superconducting TC behavior as a functionof the F-layer thickness, Josephson junctions with an intrinsic π shift across the junction, and inverted differentialI-V characteristics. In this work we report on the experimental observation of re-entrant and doubly suppressedsuperconductivity in Nb/Cu1−xNix bilayers as a function of the ferromagnetic layer thickness dCuNi (see figure). Thesuperconducting TC drops sharply with increasing dCuNi till superconductivity is suppressed at dCuNi 3.5-4 nm. Forfurther increase of the Cu1−xNix layer thickness, the superconducting state restores at dCuNi ≈ 14 nm for the re-entrant behavior (dNb ≈ 7.3 nm) [2], and dCuNi ≈ 25 nm for the doubly suppressed re-entrant behavior (dNb ≈ 6.2nm) [3]. Then, with a subsequent increase of dCuNi, the superconductivity either saturates (dNb ≈ 7.3 nm) [2] orvanishes again at dCuNi ≈ 38 nm (dNb ≈ 6.2 nm) [3]. To fabricate these samples, an improved thin-film depositiontechnique has been applied [2]. Using material parameters obtained from the fitting of the experimental data wehave made a forecast of the superconducting spin-valve effect [4, 5], which could be observed if an F/S/F trilayer isfabricated in the same technological framework as the bilayers studied in the work.

The work was partially supported by BMBF (project MDA01/007), RFBR (projects No 07-02-00963 and 08-02-90105-Mol a), and the Program of RAS “Spintronics”.

[1] A.I. Buzdin, Rev. Mod. Phys. 77, 935 (2005).[2] V.I. Zdravkov, A.S. Sidorenko, G. Obermeier, S. Gsell, M. Schreck, C. Muller, S. Horn, R. Tidecks, L.R. Tagirov,

Phys. Rev. Lett. 97, 057004 (2006).[3] V.I. Zdravkov, J. Kehrle, G. Obermeier, et al., Phys. Rev. B (submitted).[4] L.R. Tagirov, Phys. Rev. Lett. 83, 2058 (1999).[5] A.I. Buzdin, A.V. Vedyayev, and N.V. Ryzhanova, Europhys. Lett. 48, 686 (1999).

29


Arrays and circuits with SFS π-junctions. Inverse and π-periodical Josephsoncurrent-phase relations

V.V. RyazanovInstitute of Solid State Physics, Russian Academy of Sciences Chernogolovka, Moscow district, 142432, Russia

The talk is related to the one of the first successful realization of the quantum and digital circuits consistingof superconducting loops interrupted by π-junction. We use π-junctions based on superconductor–ferromagnet–superconductor (SFS) Josephson sandwiches (Nb-Cu/Ni-Nb) with high critical current density up to 104 A/cm2

which are suitable for applications as a passive superconducting phase inverters [1]. The origin of the π-state in aSFS junction is an oscillating and sign-reversing superconducting order parameter induced in the ferromagnet close tothe SF-interface due to the exchange splitting of spin-up and spin-down electron subbands in ferromagnets [2]. Theπ-state corresponds to the inverse current-phase relation and a negative junction coupling energy. The π-junctionpresence does results in the superconducting phase inversion and arising of spontaneous flux in π-junction arrays.Its inclusion into a conventional dc-SQUID allowed to observe a half-periodic shift of the external magnetic fielddependence of the π-SQUID critical current. This key experiment has shown that SFS π-junction can be insertedin any cell of Josephson digital and quantum electronics like a stationary phase inverter [3]. Moreover we foundno difference between the decoherence times of otherwise identical phase qubits with and without π-junctions. Thejunctions are based on a classical niobium thin film technology so they can be incorporated directly into existingarchitectures of superconducting electronics. We have observed also interesting behavior of the SFS π-junctionsat temperature of the π-transition where only the second sin(2ϕ)-Fourier component of the current-phase relationsurvives. Half-integer Shapiro steps and half-flux-quantum period of Fraunhofer patterns observed at the transitiontemperature were reliable evidences of the 2ϕ-component supercurrent flow.

[1] V.V. Ryazanov, V.A. Oboznov, A.Yu. Rusanov, A.V. Veretennikov, A.A. Golubov, and J. Aarts, Phys. Rev. Lett. 86, 2427(2001); V.A. Oboznov, V.V. Bolginov, A.K. Feofanov, V.V. Ryazanov, and A.I. Buzdin, Phys. Rev. Lett. 96, 197003 (2006).

[2] A.I. Buzdin, Rev. Mod. Phys. 77, 935 (2005).[3] G. Blatter, V.B. Geshkenbein, L.B. Ioffe, Phys.Rev. B 63, 174511 (2001); E. Terzioglu and M.R. Beasley,

IEEE Trans. On Appl. Supercond. 8 48 (1998); A.V. Ustinov, V.K. Kaplunenko, J. Appl. Phys. 94, 5405 (2003).

30

Sunday, June 14, afternoon

Quantum kinetic approach for studying thermal transport: calculation of the Nernsteffect

A.M. Finkel’steinDepartment of Physics, TAMU, College Station, USA and and

Department of Condensed Matter Physics, the Weizmann Institute of Science, Israel

K. MichaeliDepartment of Condensed Matter Physics, the Weizmann Institute of Science, Israel

We developed a user friendly scheme based on the quantum kinetic equation for studying thermal transport phe-nomena in the presence of interactions and disorder. This scheme is suitable for both a systematic perturbativecalculation as well as a general analysis. We believe that we present an adequate alternative to the Kubo formula,which for the thermal transport is rather cumbersome. The scheme has been applied for studying the Nernst effectin disordered films. We show that the strong Nernst signal observed recently in amorphous superconducting films farabove the critical temperature is caused by the fluctuations of the superconducting order parameter. We demonstratea striking agreement between our theoretical calculations and the experimental data at various temperatures andmagnetic fields.

31


On the microscopic origin of excess low frequency flux 1/f noise in qubits and SQUIDs

L. FaoroLaboratoire de Physique Theorique et Hautes Energies, CNRSUMR7589,Universites Paris 6 et 7, 4 place Jussieu, 75252 Paris, Cedex 05, France

At millikelvin temperatures, superconducting flux and phase qubits and SQUIDs (Superconducting QUantumInterference Devices) both suffer from intrinsic magnetic flux noise. The noise power spectrum scales as 1/fβ, wheref is frequency and β is approximately unity. Low-frequency flux noise enhances decoherence in qubits and reducesflux resolution in SQUIDs. Remarkably, all devices show approximately the same level of noise, a few µΦ0 Hz−1/2 at1 Hz; Φ0 is the flux quantum. The magnitude of the flux noise scales only weakly with the area of the device, and isindependent of temperature T .

In this talk I will illustrate our theoretical picture [1] for the excess low frequency flux noise consistent with data[2, 3] in which the noise is due to the spins at the Superconductor Insulator interface coupled via RKKY interaction. Incontrast to the alternative models [4] this mechanism explains many puzzling features of the flux noise: its apparenttemperature independence down to 20 mK, its persistence to at least 20 MHz and the rough SQUID loop areaindependence. This mechanism generates roughly 1/f noise in a broad frequency. I will report on some recentexperimental results [5, 6] that support our theoretical conjecture. I will also discuss some very recent puzzling resultsby McDermott group at University Madison Wisconsin that indicate a large and previously overlooked source of noise:fluctuations of the kinetic inductance in the superconducting wires which can be masked as a flux noise in some cases.

[1] L. Faoro and L.B. Ioffe, Phys. Rev. Lett 100, 227005 (2008).[2] F.C. Wellstood, C. Urbina, and J. Clarke, IEEE Trans. Magn. 23, 1662 (1987).[3] R.C. Bialczak et al., Phys. Rev. Lett. 99, 187006 (2007).[4] R.H. Koch, D.P. DiVincenzo, and J. Clarke, Phys. Rev. Lett. 98, 267003 (2007).[5] S. Sendelbach, D. Hover, A. Kittel, M. Muck, J.M. Martinish, and R. McDermott., Phys. Rev. Lett. 100, 22706 (2008).[6] T. Lanting et al., Phys. Rev. B. 79, 060509 (2009).

32


Pseudogaped superconductivity near mobility edge

M.V. Feigel’manL.D.Landau Institute for Theoretical Physics, Russia

L.B. IoffeDepartment of Physics and Astronomy, Rutgers University, USA

E. CuevasDepartamento de Fısica, Universidad de Murcia, Spain

V.E. KravtsovAbdus Salam International Center for Theoretical Physics, Italy

We present a semi-quantitative theory of electron pairing correlations in bulk “poor conductors” with a weakattractive Cooper interaction, at Fermi energies EF near the Anderson mobility edge Ec. An analysis is basedon analytical treatment of pairing correlations, described in the basis of exact single-particle eigenstates of the 3DAnderson model, in combination with numerical data on eigenfunction correlations. We analyzed three distinctphases of such a system: i) “critical” superconductive state formed at EF = Ec, ii) superconductive state with astrong pseudogap, realized due to pairing of weakly localized electrons (with relatively large single-particle localizationlength), and iii) insulating state realized at EF still deeper inside localized band. The emphasis in this talk will bemade on the pseudo-gaped superconductive state. The major new feature of the pseudo-gaped state is the presenceof two independent energy scales: in addition to collective superconductive gap ∆, a new energy scale ∆P comesinto play; the latter characterizes typical binding energy of localized electron pairs. Two-gap nature of the “pseudo-gaped superconductor” leads to specific features seen in scanning tunneling spectroscopy and point-contact Andreevspectroscopy. We also show that pseudo-gaped superconductive state should demonstrate strong non-conservation offull spectral weight of high-frequency conductivity. Some preliminary results of this work were published in [1].

[1] M.V. Feigel’man, L.B. Ioffe, V.E. Kravtsov, and E.A. Yuzbashyan, Phys. Rev. Lett. 98, 027001 (2007).

33


Superconductor-Insulator transition in strongly disordered superconductors.

L.B. IoffeDepartment of Physics and Astronomy, Rutgers University,

136 Frelinghuysen Road, Piscataway, New Jersey 08854, USA

I review the data on the superconductor-insulator transition in thin films and contrast it with the artificial Joseph-son arrays. I argue that although both happen against the background of the superconducting gap (in neither caseone particle excitation seem to be relevant) they belong to different classes. This imposes the restriction on pos-sible Hamiltonians that describe the physics of the strongly disordered superconducting films. I suggest the modelHamiltonian that satisfies these constraints.

I discuss the solution of the resulting theory on Bethe lattice and its solution in replica formalism. In particular, Ishow that very near the critical point the replica symmetry breaks down which corresponds to a very inhomogeneouslow temperature state. On the other side of the transition, the insulating state is formed which is characterized bylocally discrete levels. I discuss implications of these results to the physical systems.

34


Quantum divisibility test and its application in mesoscopic physics

G.B. LesovikL.D. Landau Institute for Theoretical Physics RAS, 117940 Moscow, Russia

M.V. SuslovMoscow Institute of Physics and Technology, Institutskii per. 9, 141700 Dolgoprudny, Moscow District, Russia

G. BlatterTheoretische Physik, ETH-Honggerberg, CH-8093 Zurich, Switzerland

We present a quantum algorithm to transform the cardinality of a set of charged particles flowing along a quantumwire into a binary number. The setup performing this task (for at most N particles) involves log2 N quantum bitsserving as counters and a sequential read out. Applications include a divisibility check to experimentally test thesize of a finite train of particles in a quantum wire with a one-shot measurement and a scheme allowing to entanglemulti-particle wave functions and generating Bell states, Greenberger-Horne-Zeilinger states, or Dicke states in aMach-Zehnder interferometer.

35

Monday, June 15, morning

Broken symmetry and quantum Hall ferromagnetism in suspended bilayer graphene

A. YacobyDepartment of Physics, Harvard University, 17 Oxford St., Cambridge, Massachusetts 02138, USA

Graphene and its bilayer have generated tremendous excitement in the physics community due to their uniqueand extraordinary electronic properties. The intrinsic physics of these materials, however, is partially masked bysubstrate-induced disorder in experimental samples. Here we report the fabrication of suspended bilayer graphenedevices with very little disorder. We observe quantized Hall states at magnetic fields as low as 0.1 T in these samples,as well as broken symmetry states that manifest as quantum Hall plateaus at intermediate filling factors = 0, ±1, ±2and ±3. The devices exhibit extremely high resistance in the = 0 state that grows exponentially as magnetic field isincreased and scales as magnetic field divided by temperature.

36


Graphene and Its Chemical Derivatives

K.S. NovoselovSchool of Physics and Astronomy, University of Manchester, Oxford Road, M13 9PL, Manchester, UK

When one writes by a pencil, thin flakes of graphite are left on a surface. Some of them are only one angstrom thickand can be viewed as individual atomic planes cleaved away from the bulk. This strictly two dimensional materialcalled graphene was presumed not to exist in the free state and remained undiscovered until the last year. In fact,there exists a whole class of such two-dimensional crystals. The most amazing things about graphene probably isthat its electrons move with little scattering over huge (submicron) distances as if they were completely insensitiveto the environment only a couple of angstroms away. Moreover, whereas electronic properties of other materials arecommonly described by quasiparticles that obey the Schrodinger equation, electron transport in graphene is different:It is governed by the Dirac equation so that charge carriers in graphene mimic relativistic particles with zero restmass. The very unusual electronic properties of this material as well as the possibility for it’s chemical modificationmake graphene a promising candidate for future electronic applications.

37


Graphene as an open platform for tuning 2D phase transitions

B.M. Kessler, C.O. Girit, and A. ZettlDepartment of Physics, University of California at Berkeley, Berkeley, CA, 94720 USA and

Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720 USA

V. BouchiatDepartment of Physics, University of California at Berkeley, Berkeley, CA, 94720 USA and

Institut Neel, CNRS-Grenoble, 38042 Grenoble, France

Graphene is a recently realized two-dimensional (2D) crystal with many interesting properties including a bandstructure that allows the carrier concentration to be tuned continuously between electrons and holes. The easilyaccessible 2D electron gas in graphene provides an ideal platform on which to tune, via application of an electrostaticgate, the coupling between electronically ordered dopants deposited on its surface. To demonstrate this concept,we have chosen to study an array of superconducting clusters deposited on Graphene capable to induce via theproximity effect [1] a gate tunable superconducting transition. Using a simple fabrication procedure based on metallayer dewetting, we have produced doped graphene sheets decorated with a non percolating network on nanoscaletin clusters. This hybrid material displays a two-step superconducting transition. The higher transition step is gateindependent and correspond to the transition of the tin clusters to the superconducting state. The lower transitionstep towards a real zero resistance state exhibiting a well developped supercurrent, is strongly gate-tunable and isquantitatively described by Berezinskii-Kosterlitz-Thouless 2D vortex unbinding [2, 3]. We report the details of thetransition and ground state properties of this system as a function of gate voltage, applied bias current and magneticfield [4]. Strong screening of the vortex-antivortex interaction results in an exceptionally sensitive response to appliedmagnetic fields. Our simple self-assembly method and tunable coupling can readily be extended to other electronicorder parameters such as ferro/antiferromagnetism, charge/spin density waves using similar decoration techniques.

[1] M.V. Feigel’man, M.A. Skvortsov, and K.S. Tikhonov, JETP Lett. 88, 862 (2008).[2] V.L. Berezinskii, Zh. Eksp. Teor. Fiz. 59, 207 (1970) [Sov. Phys. JETP 32, 493 (1971)].[3] J.M. Kosterlitz and D.J. Thouless, J. Phys. C-Solid State Phys. 6, 1181 (1973).

[4] B.M. Kessler, C.O. Girit, A. Zettl, and V. Bouchiat, to be published.

38


Shot noise in graphene Josephson junctions

A. Fay, F. Wu, M. Tomi, J. Wengler, and P. HakonenLow Temperature Laboratory, Helsinki University of Technology, Espoo, Finland

R. DanneauLow Temperature Laboratory, Helsinki University of Technology, Espoo, Finland and

Forschungszentrum Karlsruhe, Institut fur Nanotechnologie, Karlsruhe, Germany

M. WiesnerLow Temperature Laboratory, Helsinki University of Technology, Espoo, Finland and

Faculty of Physics, Adam Mickiewicz University, 61-614 Poznan, Poland

Non-equilibrium current fluctuations provide invaluable supplementary information to the regular conductivitymeasurements in nanoscale samples. We have studied shot noise, in graphene strips at cryogenic temperatures downto 50 mK [1]. We find that the Fano factor (F = SI/2e〈I〉) varies as a function of the carrier density and as afunction of the width to length ratio. At the Dirac point, the measured F is close to the universal value of 1/3 thatis theoretically predicted for ideal, ”pseudo-diffusive” graphene samples with W/L > 3.

Using superconducting metal contacts, gate-controlled supercurrents can be generated in graphene. These Joseph-son junctions display clear signatures of multiple Andreev reflections, which leave pronounced fingerprints into theshot noise as well as into electrical conductivity. In my presentation, I will introduce the main results of our investi-gations with superconducting contacts and discuss briefly our preliminary experiments on the current-phase relationin graphene Josephson junctions [2].

[1] R. Danneau et al., Phys. Rev. Lett. 100, 196802 (2008); R. Danneau et al., J. Low Temp. Phys. 153, 374 (2008).[2] A. Fay et al., to be published.

39


Direct detection of topological order in topological insulators via imaging ofspin-textured edge-states

M.Z. Hasan, D. Hsieh, Y. Xia, D. Qian, and L. WrayDepartment of Physics, Princeton University, Princeton, NJ

Y. Hor and R. J. CavaDepartment of Chemistry, Princeton University, Princeton, NJ

Most quantum states of condensed-matter are categorized by spontaneously broken symmetries (Landau paradigm).The remarkable discovery of charge quantum Hall effects (1980s) revealed that there exists an organizational principleof matter based not on the broken symmetry but only on the topological distinctions in the presence of time-reversalsymmetry breaking. In the past few years, theoretical developments suggest that new classes of topological states ofquantum matter might exist that are purely topological in nature in the sense that they do not break time-reversalsymmetry hence can be realized without any applied magnetic field: “Quantum Hall-like effects without magneticfield”. In this presentation, I report a series of experimental results [1–5] documenting and demonstrating the existenceof such a topologically ordered time-reversal-invariant state of matter dubbed as “Strong Topological Insulator” anddiscuss the exotic electromagnetic (Wilczek’s theta vacuum) properties this novel phase of quantum matter mightexhibit and outline their potential use.

[1] D. Hsieh et.al., Nature 452, 970 (2008).[2] Y. Xia et.al., Nature Physics 5, 398 (2009).[3] D. Hsieh et.al., Science 323, 919 (2009).[4] Y. Hor et.al., Physical Review B 79, 195208 (2009).[5] J.E. Moore, Nature Physics 5, 378 (2009).

40

Monday, June 15, afternoon

High frequency dynamics of the superconducting phase in long SNS diffusiveJosephson junctions coupled to a superconducting resonator

F. Chiodi, M.Ferrier, S. Gueron, and H. BouchiatLaboratoire de Physique des Solides Univ.Paris Sud, 91405 Orsay France

When a metallic normal wire connects two superconducting reservoirs, at sufficiently low temperature, a nondissipative current can flow through the junction. If the wire is longer than the superconducting coherence length,the amplitude and temperature decay of this supercurrent only depend on the mesoscopic parameters of the normalwire: phase coherence time and Thouless energy. Whereas the equilibrium properties of such SNS junctions arewell understood, high frequency and out of equilibrium physics are still under exploration in order to determine therelevant time scales of phase relaxation and relaxation.

In order to investigate the evolution of the current phase relation in such SNS junctions with high frequency phasedriving, we have inductively coupled one NS ring to a multimode superconducting resonator. The in- and out-of-phaseac response of the ring is deduced from the dc flux dependence of the frequency and quality factor of the resonancesfrom 300 MHz up to 6 GHz. Different behaviors are observed for frequencies below and above the inverse of thediffusion time through the N wire. When increasing the rf excitation amplitude beyond linear response, the out-of-phase (dissipative) response exhibits a strong increase near odd multiples of a half flux quantum, which correspondto the closing of the induced minigap in the N wire. These results are compared to recent theoretical findings andstimulate future similar investigations on more exotic junctions.

41


Thermal effects in hybrid superconducting nanostructures

H. CourtoisInstitut Neel, CNRS and Universite Joseph Fourier,25 avenue des Martyrs, 38042 Grenoble, France andLow Temperature Laboratory, TKK, Helsinki, Finland

S. Rajauria, L. Pascal, and B. PannetierInstitut Neel, CNRS and Universite Joseph Fourier, 25 avenue des Martyrs, 38042 Grenoble, France

A. Vasenko and F.W.J. HekkingLPMMC, Universite Joseph Fourier and CNRS, 25 avenue des Martyrs, 38042 Grenoble, France

M. Meschke, J. Peltonen, and J.P. PekolaLow Temperature Laboratory, TKK, Helsinki, Finland

We will discuss thermal effects appearing in two kinds of superconducting hybrid nanostructures.A significant electron cooling is observed in micro-coolers made of a pair of Superconductor–Insulator–Normal metal

(S-I-N) junctions biased at a voltage just below the superconducting gap. Nevertheless, this cooling appears to beless efficient at very low temperature. We have studied the electron transport properties of S-I-N-I-S micro-coolers.At very low temperature, a zero bias differential conductance peak is observed and identified as the contribution ofthe Andreev reflection. We show that the Andreev current introduces additional dissipation in the normal metal,equivalent to Joule heating. By analyzing quantitatively the heat balance, we provide a full description of the evolutionof the electronic temperature with the voltage.

We investigated the hysteresis occurring in the current-voltage characteristic of Superconductor–Normal metal–Superconductor (S-N-S) junctions at very low temperature, whereas no hysteresis is expected in such overdampedJosephson junctions. We have studied S-N-S junctions including additional superconducting tunnel probes. We havethus been able to measure the normal metal electron temperature as a function of the bias conditions, i.e. in boththe hysteretic and the reversible regimes. Our results demonstrate unambiguously that the hysteresis results from theincrease of the normal metal electron temperature once the junction switches to the resistive state. In this regime,an electron temperature of up to 0.6 K is measured while the thermal bath remains at 50 mK. We have devised aquantitative model including the electron-phonon coupling and the superconducting electrodes thermal conductance.

[1] S. Rajauria, P. Gandit, T. Fournier, F.W.J. Hekking, B. Pannetier, and H. Courtois, Phys. Rev. Lett. 100, 207002 (2008).[2] H. Courtois, M. Meschke, J. Peltonen, and J.P. Pekola, Phys. Rev. Lett. 101, 067002 (2008).

42


Out-of-equilibrium Josephson effect in Al/AlOx/Ti and V/AlOx/Al superconductingtunnel nanostructures

F. GiazottoNEST CNR-INFM & Scuola Normale Superiore, I-56126 Pisa, Italy

We will review some recent advances in out-of-equilibrium control of quasiparticle dynamics as well as Josephsoncoupling manipulation in superconducting tunnel nanostructures [1]. To this end, in the first part of this presentationwe will show experimental results concerning control of the supercurrent in Al/AlOx/Ti Josephson junctions byinjecting quasiparticles in a Ti island from two additional tunnel-coupled Al superconducting reservoirs [2]. Bothenhancement and quenching of the supercurrent with respect to equilibrium are achieved. We demonstrate cooling ofthe Ti island by quasiparticle injection from the normal state deep into the superconducting phase. A model basedon heat transport and non-monotonic current-voltage characteristic of a Josephson junction satisfactorily accountsfor these findings.

In the second part of the presentation we will show results obtained on V-based Josephson junctions. In particular,we will report the fabrication of planar V/Cu/V mesoscopic Josephson weak-links of different size, and the analysisof their low-temperature behavior [3]. The shorter junctions exhibit critical currents of several tens of µA at 350 mK,while Josephson coupling persists up to ∼ 2.7 K. Good agreement is obtained by comparing the measured switchingcurrents to a model which holds in the diffusive regime. Such results demonstrate that V is an excellent candidatefor the implementation of superconducting nanostructures operating at a few Kelvin. We will conclude by showingsome preliminary measurements obtained in V/AlOx/Al Josephson tunnel junctions both in equilibrium and out-of-equilibrium conditions. In the latter case Josephson coupling is controlled and manipulated through quasiparticleinjection in an Al island from additional tunnel-coupled superconducting junctions, and shows features peculiar ofcooling as well as heating regimes.

[1] F. Giazotto, T.T. Heikkila, A. Luukanen, A.M. Savin, and J.P. Pekola, Rev. Mod. Phys. 78, 217 (2006).[2] S. Tirelli, A.M. Savin, C. Pascual Garcia, J.P. Pekola, F. Beltram, and F. Giazotto, Phys. Rev. Lett. 101, 077004 (2008).[3] C. Pascual Garcıa and F. Giazotto, Appl. Phys. Lett. 94, 132508 (2009).

43


Relaxation of Non-Equilibrium Quasiparticles in a Superconductor at Ultra-LowTemperatures

K. Arutyunov and H.-P. AuranevaNanoScience Center, Department of Physics, University of Jyvaskyla?, 40014, Jyvaskyla, Finland

When an electron enters a superconductor it takes some time (distance) to find a matching particle to form an equi-librium Cooper pair. Though the subject has been studied intensively since mid-70s [1], mainly the high temperaturelimit T’Tc has been investigated. There is a very poor understanding of the phenomena at low temperatures whenthe energy gap is much higher than the temperature. Additionally, due to microfabrication limitations at that time nospatial resolution of the phenomena has been investigated. Here we present the results on experimental study of thespatially-resolved relaxation of the non-equilibrium quasiparticles at ultra-low temperatures. Multi-terminal tunnelnanostructures (Fig. 1, left) were fabricated and measured down to T = 20 mK. The electrons were injected into asuperconductor through a tunnel barrier from a normal metal or a ferromagnetic at a current Iinj, and the Idet(Vdet,Iinj = const) dependencies of a ‘detector’ single NIS or double NISIN tunnel junction away from the ‘injector’ weremeasured.

FIG. 1: (Left) Schematic of the experiment. (Right) Increase of the effective electron temperature Te = Te − Tbath withinthe locus of the detector as function of the distance L between the detector and the injector. Symbols correspond to variousinjection currents (voltages). Lines are guides to the eye.

There is a certain correlation between the proximity of the detector to the injector L, the injector current Iinj andthe shape of the detector’s I-V characteristic. The effect can be understood by deviation of the superconductor DOSand the distribution function from its equilibrium. In the simplest approximation, the non-equilibrium state can becharacterized by the spatially and injection current dependent: (1) non-zero chemical potential difference betweenthe condensate and the quasiparticles; (2) increase of the effective electron temperature Te; and (3) broadening ofthe DOS. An example of the dependence of the effective electron temperature Te on the injection current Iinj andthe proximity to the injector L is presented in Fig. 1, right. Apart from the basic science interest, the subject is ofsignificant importance for various applications: e.g. NIS coolers and cold/hot electron bolometers.

[1] Nonequilibrium superconductivity, phonons, and Kapitza boundaries, edited by K.E. Gray (Plenum Press, NY, 1981).

44


Nonstationary Josephson-like effects in SINIS junction

K.S. TikhonovL.D. Landau Institute for Theoretical Physics RAS, 117940 Moscow, Russia and

Moscow Institute for Physics and Technology, 141700, Dolgoprudny, Russia

M.V. Feigel’manL.D. Landau Institute for Theoretical Physics RAS, 117940 Moscow, Russia

Non-stationary coherent effects are considered in superconductor-normal metal-superconductor structure with rel-atively strong normal scattering on S/N interfaces (interface resistance is large compared to intrinsic resistance of Nmetal). Analytical expressions are found for the time-dependent anomalous Green functions induced in the N regionunder the fixed-voltage-bias. The amplitude of the current oscillations is determined in non-equilibrium conditions,reproducing results of Aslamazov, Larkin and Ovchinnikov [1]. Non-stationary correction to the distribution functionand to the electrical current are calculated and found to be slowly decreasing with effective temperature of electrons inthe normal wire, leading to the dominance of the second-harmonic term in the Josephson current, Is(t) ∝ sin(4eV t) athigh temperature and low voltage (qualitatively analogous effect was discussed in [4, 6], and experimentally observedby Courtois [2]). The notion of the “effective capacitance” [5] and hysteretic properties of SNS junctions [3, 5] arediscussed.

[1] L. Aslamazov, A. Larkin, and Yu. Ovchinnikov, Zh. Eksp. Theor. Phys. 55, 323 (1986).[2] H. Courtois, Ph. Gandit, D. Mailly, and B. Pannetier, Phys. Rev. Lett. 76, 130 (1996).[3] H. Courtois, M. Meschke, J. Peltonen, and J. Pekola, Phys. Rev. Lett. 101, 067002 (2008).[4] N. Argaman, Superlattices and microstructures 25, 861 (1999).[5] L. Angers, F. Chiodi, G. Montambaux, M. Ferrier, S. Gueron, H. Bouchiat, and J. Cuevas, Phys. Rev. B 77, 165408 (2008).[6] F. Zhou and B. Spivak, Pis’ma v ZhETF 65, 347 (1997).

45

Tuesday, June 16, morning

Scattering of electromagnetic waves on a single artificial atom

O. Astafiev, Yu.A. Pashkin, T. Yamamoto, Y. Nakamura, and J.S. TsaiThe Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan

NEC Nano Electronics Research Laboratories. Tsukuba, Ibaraki, 305-8501, Japan andCREST-JST, Kawaguchi, Saitama 332-0012, Japan

A.A. Abdumalikov and K. InomataThe Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan and

CREST-JST, Kawaguchi, Saitama 332-0012, Japan

A.A. ZagoskinDepartment of Physics, Loughborough University, Loughborough, LE11 3TU Leicestershire, UK

We demonstrate resonant electromagnetic wave scattering on an artificial quantum system (a single artificial atom)in a 1D-transmission line. The atom, nominally the same as the flux Josephson-junction qubit, contains a set ofquantized energy levels. Our scatterer is a macroscopic object of about 1 µm size, consisting of 1010 natural atoms,nevertheless, it reveals quantum properties in wave scattering. We study elastic and inelastic parts of the scatteredwaves. The single atom shows anomalous “susceptibility” behavior near the atomic absorption line. Spectrum ofinelastically scattered waves exhibits the resonance fluorescence triplet. The “atom”, interacting with the environment(1D-transmission line) solely electromagnetically, is the simplest example of an open quantum system. Having theclosest analog of a natural atom in the free space, it opens up an opportunity to observe a series of fundamentalphenomena from quantum optics. Using the artificial atom, we have already demonstrated a series of quantumoptical phenomena, among them, resonant fluorescence, spontaneous and stimulated emission, electromagneticallyinduced transparency and others.

46


Coupling superconducting qubits using sideband transitions in circuit QED

P.J. Leek, M. Baur, S. Filipp, and A. WallraffQuantum Device Lab, Department of Solid State Physics, ETH Zurich, Switzerland

In circuit quantum electrodynamics, superconducting quantum bits are coupled to microwave photons on a trans-mission line resonator [1]. The ultra-strong coupling and accurate control possible in this solid state realisation ofcavity QED has led to a wide variety of on-chip quantum optics and computation experiments in recent years. In thistalk I will present recent experimental results on the use of sideband transitions between superconducting qubits andresonator photons in circuit QED for the generation of a potentially scalable qubit-qubit coupling [2, 3].

[1] A. Wallraff et al., Nature 431, 162 (2004).[2] P.J. Leek et al., arXiv:0812.2678, to be published in Phys. Rev. B (2009).[3] S. Filipp et al., Phys. Rev. Lett. 102, 200402 (2009).

47


Microwave interferometry with a superconducting artificial atom

J. Bylander, D.M. Berns, L.S. Levitov, and T.P. OrlandoMassachusetts Institute of Technology

S.O. ValenzuelaMassachusetts Institute of Technology and

Presently: ICREA and CIN2 ICN/CSIC, Barcelona

M.S. RudnerMassachusetts Institute of Technology and

Presently: Harvard University

A.V. ShytovUniversity of Utah

K.K. BerggrenMIT Lincoln Laboratory and

Massachusetts Institute of Technology

W.D. OliverMassachusetts Institute of Technology and

MIT Lincoln Laboratory

Superconducting persistent-current qubits are artificial atoms with multiple energy levels. In the presence of large-amplitude excitation, the system can be coherently driven through one or more of the energy-level avoided crossings.The resulting Landau-Zener-Stuckelberg (LZS) transitions mediate a rich array of quantum-coherent phenomena.

In this talk I will begin with a review of LZS transitions at a single level-avoided crossing, where we observedMach-Zehnder-type quantum interference fringes in the rates for n-photon transitions, with n = 0 . . . 50 [1, 2].

By driving transitions to a third level and relying on the fast relaxation to the ground state, we demonstratedmicrowave-induced cooling. We achieved an affective qubit temperature < 3 mK: a factor 10−100 lower than thedilution refrigerator ambient temperature [3]. Employing this technique, we were able to drive transitions betweenlevels separated by only 10 MHz (0.5 mK), more than an order of magnitude lower than the thermal energy of thebath (20 mK).

Further extending the driving amplitude to reach across several level-avoided crossings, we probed the artificialatom’s energy spectrum over the bandwidth 0.01−120 GHz, while driving it at a fixed frequency of only 0.16 GHz.We call this approach “amplitude spectroscopy,” as we monitor the system’s response to amplitude rather thanfrequency [4].

Finally, by applying a waveform consisting of two harmonic components, we demonstrated a mapping between theamplitude and phase of the harmonics produced at the source and those received by the device. This mapping allowedus to image the actual waveform at the device and accurately shape it to produce the desired time dependence [5].

These experiments exhibit a remarkable agreement with theory, and are extensible to other solid-state qubit modal-ities. In addition to our interest in these techniques for fundamental studies of quantum coherence in strongly-drivensolid-state systems, we anticipate that careful engineering of the driving protocol will find application to non-adiabaticqubit control and state-preparation methods for quantum information science and technology.

[1] W.D. Oliver et al., Science 310, 1653 (2005).[2] D.M. Berns et al., Phys. Rev. Lett. 97, 150502 (2006).[3] S.O. Valenzuela et al., Science 314, 1589 (2006).[4] D.M. Berns et al., Nature 455, 51 (2008).[5] J. Bylander et al., arXiv:0812.4670 (2008).

48


Non-projective measurement of solid-state qubits: theory and experiments

A.N. KorotkovUniversity of California, Riverside and

Moscow State University

Non-projective (weak) quantum measurement of single quantum systems is becoming an attractive topic in meso-scopic physics. In contrast to the ensemble measurement, which neglects the output information and is usuallydescribed by decoherence, the quantum state of a single system may remain pure in the process of measurement,and its evolution (gradual collapse) is directly related to the acquired information. In the talk I will review thesimple theory [1] describing such measurement for a qubit, emphasizing various derivations of the theory and neededassumptions. So far three confirming experiments on non-projective collapse of solid-state qubits have been realized:partial collapse of a superconducting phase qubit [2], uncollapse (measurement undoing) for a phase qubit [3], andnon-decaying Rabi oscillations in a superconducting charge qubit revealed via the output spectrum [4].

[1] A.N. Korotkov, Phys. Rev. B 60, 5737 (1999); 63, 115403 (2001).[2] N. Katz et al., Science 312, 1498 (2006).[3] N. Katz et al., Phys. Rev. Lett. 101, 200401 (2008).[4] A. Palacios-Laloy et al., unpublished.

49


Weak continuous measurements of multiqubits systems

E. Il’ichevInstitute of Photonic Technology, P.O. Box 100239, 07702 Jena, Germany

For superconducting qubits we have proposed and realized a weak continuous readout which belongs to the classof quantum non-demolition measurements. Moreover, our scheme enables to measure a superconducting qubit at thedegeneracy point where a qubit is in a superposition of two classical states. In this scheme, the superconductingoscillator coupled to superconducting qubit is used as a detector of the qubit’s state. Such system is analogue toa system of a single atom interacting with photons in a cavity, which allows to study quantum electrodynamics inartificial macroscopic systems. Pushing this analogy we demonstrate Sisyphus cooling and amplification caused byenergy exchange between an oscillator and a flux qubit.. Using the Sisyphus effect we show consistency between theadiabatic weak continuous measurement in the ground state and the spectroscopic measurement. This allows us tocharacterize the more complicated system of coupled qubits by making use of the same method. We have realized andstudied fixed ferromagnetic, antiferromagnetic as well as tunable qubit/qubit coupling. We argue that ground statemeasurements can be used for characterization of entangled states in coupled flux qubits.

50


Period-doubling quantum detector

A.B. ZorinPTB, Braunschweig, Germany

Yu. MakhlinLandau Institute for Theoretical Physics, Chernogolovka, Russia

We propose a threshold detector, based on a parametric bifurcation amplifier in an externally pumped nonlinear-oscillator circuit. The ac-driven resonance circuit includes a dc-biased Josephson junction for the parametric frequencyconversion (bifurcation with doubling of the period) due to its nonlinearity. A sharp onset of oscillations at a half ofthe drive frequency allows one to detect a small variation of the parameters of the circuit and, in particular, to detectthe state of a Josephson quantum bit. We characterize the operation of a quantum detector based on this device.

51

Poster session

Tunable “quantum-size” effect for superconducting condensate in nonuniformmagnetic field

A.Yu. AladyshkinINPAC, Institute for Nanoscale Physics and Chemistry,

Nanoscale Superconductivity and Magnetism and Pulsed Fields Group,K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium and

Institute for Physics of Microstructures, Russian Academy of Sciences, 603950 Nizhny Novgorod, GSP-105, Russia

W. Gillijns, A.V. Silhanek, Schildermans, J. Van de Vondel, and V.V. MoshchalkovINPAC, Institute for Nanoscale Physics and Chemistry,

Nanoscale Superconductivity and Magnetism and Pulsed Fields Group,K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium

The results of theoretical and experimental investigations of the peculiarities of the nucleation of superconductivityin the presence of a nonuniform magnetic field induced by ferromagnetic films or dots with out-of-plane magneticanisotropy are presented. It is shown that the phase transition line of flux-coupled superconductor–ferromagnethybrids in the H–T plane (H is an external magnetic field and T is temperature) is determined substantially bythe spatial distribution of nonuniform magnetic field. The stray fields of the ferromagnetic structures confine thesuperconducting condensate and, accordingly, modify the condition for the nucleation of superconductivity. Thisfinding can be interpreted in terms of the quantum-size effect for Cooper pairs in a inhomogeneous magnetic field.By switching between different magnetic states of the ferromagnet, this confinement can be tuned at will, therebyreversibly changing the dependence of the critical temperature Tc on H . In particular, continuous evolution from aconventional linear Tc(H) dependence with a single maximum to a reentrant superconducting phase boundary withmultiple Tc peaks has been demonstrated.

[1] W. Gillijns, A.Yu. Aladyshkin, M. Lange, M.J. Van Bael, V.V. Moshchalkov, Phys. Rev. Lett. 95, 227003 (2005).[2] A.Yu. Aladyshkin and V.V. Moshchalkov, Phys. Rev. B, 74, 064503 (2006).[3] W. Gillijns, A.Yu. Aladyshkin, A.V. Silhanek, and V.V. Moshchalkov, Phys. Rev. B, 76, 060503(R) (2007).[4] N. Schildermans, A.Yu. Aladyshkin, A.V. Silhanek, J. van de Vondel, and V.V. Moshchalkov, Phys. Rev. B, 77, 214519

(2008); Virt. J. of App. of Supercond. (2008).[5] A.Yu. Aladyshkin, A.V. Silhanek, W. Gillijns, and V.V. Moshchalkov, Supercond. Science and Tech., submitted (2009).

52

Poster session

Coherent transport and nonlocal effects in nanofabricated Al/Cu/Al junctions

T.E. Golikova, I.E. Batov, and V.V. RyazanovInstitute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia

D. BeckmannInstitute of Nanotechnology, Research Centre Karlsruhe, 76021 Karlsruhe, Germany

The planar Al/Cu/Al submicron-size Josephson structures are investigated at low temperatures. It is found that thecurrent-voltage characteristics become hysteretic as temperature decreases (see also [1]), despite the high transparencyof SN interfaces. In the resistive part of the current-voltage characteristics, the features related to the multiple AndreevGolikova-reflection are detected. The nonlocal SNS junction voltage is observed when quasiparticles are injected intoone of the superconducting electrodes so that the total transport current through the junction is zero. The similarexperiment in ”sandwich” geometry was made before in the work [2].

[1] H. Courtois, M. Meschke, J.T. Peltonen, and J.P. Pekola, Phys. Rev. Lett. 101, 067002 (2008).[2] V.K. Kaplunenko and V.V. Ryazanov, Phys. Lett. 110A, 3 (1985).

53

Poster session

Hybrid single-electron transistor as a source of quantized electric current

J.P. Pekola, S.G. Kafanov, and M. MeschkeLow Temperature Laboratory, Helsinki University of Technology, P.O. Box 3500, 02015 TKK, Finland

A. KemppinenLow Temperature Laboratory, Helsinki University of Technology, P.O. Box 3500, 02015 TKK, Finland and

Centre for Metrology and Accreditation (MIKES), P.O. Box 9, 02151 Espoo, Finland

V. MaisiCentre for Metrology and Accreditation (MIKES), P.O. Box 9, 02151 Espoo, Finland

M. Mottonen and O.-P. SairaLow Temperature Laboratory, Helsinki University of Technology, P.O. Box 3500, 02015 TKK, Finland and

Department of Engineering Physics/COMP, Helsinki University of Technology, P.O. Box 5100, 02015 TKK, Finland

D.V. AverinDepartment of Physics and Astronomy, Stony Brook University,

SUNY, Stony Brook, New York 11794-3800, USA

Yu.A. Pashkin and J.-S. TsaiNEC Nano Electronics Research Laboratories, RIKEN Advanced Science Institute,

34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan

S.V. Lotkhov and A.B. ZorinPhysikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany

We present a hybrid normal-metal-superconductor turnstile in the form of a one-island single-electron transistorwith one gate [1]. The device demonstrates robust current plateaus at multiple levels of ef at frequency f . Wediscuss the various error mechanisms, based on our experiments and theoretical considerations [2–4]. Ultimatelythe quantization accuracy is expected to be limited by either two-electron tunneling or by Cooper-pair-electron co-tunneling. We predict based on our experiments and the theoretical considerations that it should be possible toachieve the metrological accuracy of 10−8, while maintaining the quantized current on the level above 10 pA, justby one turnstile with realistic parameters using aluminium as a superconductor. A parallel configuration of severalturnstiles yields larger current levels.

[1] J.P. Pekola, J.J. Vartiainen, M. Mottonen, O.-P. Saira, M. Meschke, and D.V. Averin, Nature Phys. 4, 120 (2008).[2] A. Kemppinen, M. Meschke, M. Mottonen, D.V. Averin, and J.P. Pekola, arXiv:0803.1563 (2008).[3] A. Kemppinen, S. Kafanov, Yu.A. Pashkin, J.S. Tsai, D.V. Averin, and J.P. Pekola, Appl. Phys. Lett. 94, 172108 (2009).[4] D.V. Averin and J.P. Pekola, Phys. Rev. Lett. 101, 066801 (2008).

54

Poster session

Inverse Faraday effect in chaotic quantum dots

M. PolianskiNiels Bohr Institute, NBIA, Blegdamsvej 17, DK-2100 Copenhagen Denmark

Classical Faraday effect, a rotation of light polarization by magnetic field, has its inverse (IFE): a strong electricfield E at frequency ω breaks time-reversal symmetry(TRS) and magnetizes the sample. If ac voltage Vω is generatedthrough a diffusive medium, the resulting IFE magnetic flux is Φcl ∼ Φ0(eVω)2mv3

F/137(hω)3c, ωτ ≫ 1.Is it possible to enhance magnetic sensitivity to E-field and detect it? A much stronger sensitivity of mesoscopic

transport to weak magnetic fields that break TRS could be used. The magnetization flux Φ results in resistanceasymmetry, and the TRS-breaking can be detected in a multi-terminal setup as Hall resistance RH . For magnetic fluxΦ through a sample it was shown that RH(Φ) = RT

H(−Φ), ifT denotes a measurement with current- and voltage-probestransposed. Chepelianskii and Bouchiat showed that this relation is violated, if TRS is broken by ac perturbationsat frequency ω [1]. Measured RH(0) 6= RT

H(0) can be interpreted as IFE-magnetization of the sample [2].We develop the theory that evaluates IFE in a chaotic quantum dot subjected to ac perturbations at frequency ω in

the absence of applied magnetic field, H = 0. Finding how asymmetry RH −RTH responds to Φ ≪ Φ0 and evaluating

this difference with ac perturbations applied, we estimate mesoscopic (sample-to-sample) fluctuations of the inducedflux Φ. Typically Φ ∼ ±Φ0(eVω/ǫ)2, ǫ = max hω, h/τd, T ≫ eVω, where τd is the dwell time of electrons and T isthe temperature. We consider in detail how IFE is affected by screening and floating probes present in experiment,and compare our predictions with experiment of Ref. 1.

[1] A.D. Chepelianskii and H. Bouchiat, Phys. Rev. Lett. 102, 086810 (2009).[2] V.M. Edelstein, Phys. Rev. Lett. 95, 156602 (2005).

55

Poster session

Combined method for the realization of φ-junction with a ferromagnetic weak link

N. PugachM.V. Lomonosov Moscow State University, 119992 Moscow, Russia

E. Goldobin, D. Koelle, and R. KleinerPhysikalisches Institut-Experimentalphysik II and Center for Collective Quantum Phenomena, Universitat Tubingen, Germany

It was established [1, 2], that in the long Josephson junction, consisted of the alternating 0 and π-junctions, theeffective second harmonic generated in the current-phase relation for the long-range phase. Its value is always negative.It is a result of the averaging over the short-range phase, that changes on a distance of the length of 0 and π-regionsa. It is assumed that a < λJ , where λJ is the Josephson penetration depth of the 0 or π-part. The effective secondharmonic has a maximum value if 0 and π-regions have the same length a ∼ λJ and close absolute values of thecritical current [2, 3]. The simplest way to create 0 and π-junctions is use of SFS junctions (S — superconductor,F — ferromagnet) with different thicknesses d0 and dπ of the F-layer [4].

If the second harmonics has a negative and large enough value, the long Josephson junction may have a groundstate with the phase shift equal by φ, 0 < φ < π, so-called φ-junction. It has to possess many unusual properties [3].But the effective second harmonic value is large enough only if 0 and π-regions has very close absolute values of thecritical current, that demands to choose d0 and dπ with very high precision. Therefore, the φ-junction is very difficultto realize by this way.

In some cases the SFS Josephson junction have non-sinusoidal current phase relation [5, 6]. Different theoreticalmodels [7–12] give somewhat similar results: the second harmonic oscillates and decreases with the ferromagneticthickness d twice rapidly than the first one. Near 0–π transition, where it is large in comparison with the firstharmonics, it is always positive, that except the φ ground state for such junction. The question is: what is happenedif every part of the long 0–π Josephson junction has the intrinsic second harmonics, or in general, non-sinusoidalcurrent-phase relation?

The Josephson current of every 0 and π part, as an odd function of the phase, can be expanded in a series ofharmonics and the problem is solved in the general form by the averaging over short-range phase as in ref. [1, 2]. Thenumber N of harmonics, that is reasonable to take into account, follows from the estimation of the short-range phase.Then, keeping terms of the same order, we obtain N+1 effective harmonics for the long 0–π Josephson junction.

Different mechanisms, giving the significantly non-sinusoidal current-phase relation of SFS junctions are analyzed.Such current-phase relation is peculiar to pure SFS junctions [9, 13], to the structure in the “dirty” limit in thepresence of parallel spin-flip scattering in the F-layer [8]. It could be realized by introducing of a thin dielectricspacer into the junction with the certain transparency of S/F interface [12]. Non-sinusoidal current-phase relationalso appears in the model taking into account s-d scattering in the ferromagnet [11, 12]. The best result is obtainedfor the pure SFS junction at low temperature. In this case, there are much more large regions of parameters values (incomparison with the description taking into account only the first harmonic) where the long 0–π Josephson junctionhas φ-ground state. Moreover, such structure may have two different ground states (two local minima of the Josephsonenergy as a function of the phase): 0 and π, 0 and φ, or φ and π. This analysis gives some practical recommendationsfor the φ-junction creation.

[1] R.G. Mints Phys. Rev. B 57, R3221 (1998).[2] A.I. Buzdin and A.E. Koshelev, Phys. Rev. B 67, 220504 (2003).[3] E. Goldobin, D. Koelle, R. Kleiner, and A. Buzdin, Phys. Rev. B 76, 224523 (2007).[4] V.V. Ryazanov, V.A. Oboznov, et al. Phys. Rev. Lett. 86, 2427 (2001).[5] V.V. Ryazanov et al., proceedings of XII Symposium “Nanophysics and Nanoelectronics” Nizhniy Novgorod, 1, 42 (2008).[6] H. Seiller, C. Baraduc, F. Lefloch, and R. Calemczuk, Phys. Rev. Lett. 92 257005 (2004).[7] A.A. Golubov, M.Yu. Kupriyanov, and E. Il’ichev, Rev. Mod. Phys. 76, 411 (2004).[8] A.I. Buzdin, Phys. Rev. B 72, 100501(R) (2005).[9] F. Konschelle, J. Cayssol, and A. Buzdin, arXiv:0807.2560 (2008).[10] A.V. Vedyayev, N. Ryzhanova, and N. Pugach, J. Magn. Magn. Mat. 305, 53 (2006).[11] N. Klenov, V. Kornev, et al. J. Phys: Conf. Ser. 97, 012037 (2008).[12] A.A. Golubov and M.Yu. Kupriyanov, Pis’ma v ZhETF 81, 419 (2005).[13] A.I. Buzdin, L.N. Bulaevskii, and S.V. Panyukov, Pis’ma ZhETF 35, 147 (1982).

56

Poster session

Breakpoint features in current voltage characteristics of intrinsic Josephson junctions

Yu. ShukrinovBLTP, JINR, Dubna, Moscow Region, 141980, Russia and

PTI, Dushanbe, 734063 Tajikistan

A phase dynamics of intrinsic Josephson junctions (IJJ) in the high temperature superconductors is theoreticallystudied. The current-voltage characteristics (CVC) of IJJ are numerically calculated in the framework of capacitivelycoupled Josephson junctions model with diffusion current [1]. The CVC show that their branches have a breakpointand some breakpoint region (BPR) before transition to another branch [2]. The breakpoint current is determinedby the creation of the longitudinal plasma wave with a definite wave number, which depends on the coupling anddissipation parameters, the number of junctions in the stack, and the boundary conditions. We find that the behaviorof the superconducting current in the coupled system of Josephson junctions is essentially different from that of asingle Josephson junction. It is demonstrated that superconducting current in the stack of IJJ reflects the mainfeatures of the breakpoint region; in particular, the fine structure in the CVC. We study various correlation functionsin the characteristics, and observe that the correlations amongst the charge on different superconducting layers andcorrelations in the superconducting currents of different junctions lead to the detailed features of CVC in the BPR,and also provides additional information about the phase dynamics in the IJJ. We present a detailed analysis of finestructure in the BPR and discuss the influence of the boundary conditions and number of junctions in the stack onthe BPR structure.

This research was supported by Russian Foundation for Basic Research, grant #08-02-00520-a.

[1] Yu.M. Shukrinov, F. Mahfouzi, P. Seidel., Physica C449, 62 (2006).[2] Yu.M. Shukrinov, F. Mahfouzi, Phys. Rev. Lett. 98, 157001 (2007).[3] Yu.M. Shukrinov, F. Mahfouzi, M. Suzuki, Phys. Rev. B 78, 134521 (2008).

57

Poster session

Transport in an array of Josephson junctions in the insulating state

S.V. Syzranov and K.B. EfetovTheoretische Physik III, Ruhr-Universitat Bochum, D-44801 Bochum, Germany

I.L. Aleiner and B.L. AltshulerPhysics Department, Columbia University, New York, N.Y. 10027, USA

We study low-temperature transport in a disordered Coulomb-blockaded Josephson junction array. The conductivityof the system is determined by the thermally activated single-Cooper-pair excitations and thus is exponentially smallin temperature with the activation energy close to the charging energy of a Cooper pair on a superconductive island.In case of sufficiently weak disorder we calculate the Drude-like contribution to the conductivity and obtain weaklocalization corrections. At a stronger disorder or lower temperatures one arrives at the Anderson localization of theexcitations. In a system with localized single-Cooper-pair states we also expect the drop of the conductivity at acertain temperature due to the many-body Anderson localization of excitations.

58

Poster session

Finite size effects on magnetic flux penetration into YBCO/LSMO hybrids

L.S. UspenskayaInstitute of Solid State Physics RAS, Chernogolovka, Russia

T. Nurgaliev and S. MitevaInstitute of Electronica BAS, Sofia, Bulgaria

The attractive idea to create artificial superconductor/ferromagnet heterostructures (SC/FM) for easy control ofthe superconductor properties by magnetic field is widely considered last decade. Of a special interest for applicationsare the HTSC/FM heterostructures, particularly the YBCO/LSMO, where the magnetization value of LSMO could beadjusted by doping, by variation of oxygen content, and magnetic domain structure could be controlled by reasonablemagnetic field. The influence of manganite on the critical current and superconducting transition temperature werestudied previously. In this work we concentrate on the in-plane field penetration into the YBCO/LSMO hybrid film,which is of practical interest as the in-plane field easier saturate the magnetic film. The study is performed by themagneto-optic visualization technique at T down to 7 K. We found a striking transformation of the in-plane externalfield into a wave of alternating perpendicular flux, the particular features of which depended on the temperature andmagnetic prehistory at temperature above superconducting transition. To shed light on the mechanism of the effect,we have investigated the magnetic domain pattern of manganite film and it’s transformations due to variations oftemperature and application of the external field. The results are discussed taking into account the finite size of thehybrid structure and the magnetostatic field distribution.

The study is supported by program of RAS “Physics of condence matter” and by RFBR grant #09-02-00856.

59

Poster session

Electron cooling by diffusive NIS tunnel junctions

A.S. Vasenko and F.W.J. HekkingLPMMC, Universite Joseph Fourier and CNRS, 25 Avenue des Martyrs, BP 166, 38042 Grenoble, France

E.V. BezuglyiB. Verkin Institute for Low Temperature Physics and Engineering, Kharkov 61103, Ukraine

H. CourtoisInstitut Neel , Universite Joseph Fourier and CNRS,

25 Avenue des Martyrs, BP 166, 38042 Grenoble, France

The flow of electric current in NIS (Normal metal–Insulator–Superconductor) tunnel junctions is accompanied bya heat transfer from the normal metal into the superconductor. This effect enables the refrigeration of electrons inthe normal metal. Two tunnel junctions arranged in a symmetric configuration (SINIS) routinely give a reduction ofthe electron temperature from 0.3 K to about 0.1 K [1]. This significant temperature reduction gives a perspectiveto use NIS junctions for on-chip cooling of nano-sized systems like high-sensitivity detectors and quantum devices.Therefore it is important to understand possible limitations of NIS refrigeration.

It this contribution we discuss two possible limitations among others. First originates from backtunneling of thenonequilibrium quasiparticles from the superconductor to the normal metal [2]. This effect occurs in nonreservoirjunction geometries typical for the experiment, for example NIS′S, where S′ is a nonequilibrium superconducting leadconnected to the superconducting reservoir (S). Nonequilibrium quasiparticles accumulated in the S′ lead can tunnelback to the N electrode. This effect can be supressed when the whole S lead of the NIS microcooler can be consideredas a reservoir [2].

But the main limitation for NIS microcoolers lies in the intrinsic nature of the current transport in the NIS junction.The transfer of quasiparticles across the NIS junction is governed by two processes: single and two particle (Andreev)tunneling. Andreev current IA generates a Joule heating IAV that is deposited in the normal metal electrode [3]. Atlow temperatures this heating dominates over single particle cooling. Therefore at given tunnel barrier transparencythe interplay between single particle tunneling and Andreev reflection sets a limiting temperature of the refrigeration.Below this temperature the electron temperature in the normal metal electrode increases for all bias voltages due tothe Andreev current generated Joule heating. We discuss this temperature of crossover from heating to cooling andthe optimization of the NIS microcooler.

[1] M.M. Leivo, J.P. Pekola, and D.V. Averin, Appl. Phys. Lett. 68, 1996 (1996).[2] A.S. Vasenko and F.W.J. Hekking, J. Low Temp. Phys. 154, 221 (2009).[3] S. Rajauria, P. Gandit, T. Fournier, F.W.J. Hekking, B. Pannetier, and H. Courtois, Phys. Rev. Lett. 100, 207002 (2008).

60

Poster session

Sign reversal of vortex motion in strongly driven vortex matter

D. VodolazovInstitute for Physics of Microstructures, Russian Academy of Sciences, 603950, Nizhny Novgorod, GSP-105, Russia

We discuss the recent experiment on nonlocal response in low-pinning NbGe superconductor. In case of largetransport current we found strong influence of the nonequilibrium effects (shrinking the vortrex core due to Larkin-Ovchinnikov effect at T ∼ Tc and local Joule heating of electron subsystem at T ≪ Tc) on nonlocal current-voltagecharacteristics. At T ∼ Tc vortices move in direction of the place with locally applied current and at T ≪ Tc they movein opposite direction. The direction of their motion at T ∼ Tc is connected with local (in the place where the transportcurrent is applied) decreasing the vortex density (due to nonequilbrium enhancement of the superconductivity nearthe vortex cores). The direction of the vortex motion at T ≪ Tc is connected with local increase of the electronictemperature (due to Joule heating) resulting in increasing the local vortex density.

61

Poster session

Anomalous transition temperature oscillations in LOFF state

A.A. Zyuzin and A.Yu. ZyuzinA.F. Ioffe Physico-Technical Institute of Russian Academy of Sciences, 194021 St. Petersburg, Russia

We consider Aharonov-Bohm effect at normal metal-inhomogeneous LOFF superconducting state transition. Itis shown that magnetic flux can increase the transition temperature and AB oscillations can have the double-peakstructure at one period. Expressions for fluctuational heat capacity and persistent current are calculated for a thinring and a cylinder. We also discuss the effect of fluctuations interaction in the nonuniform states in the vicinity ofthe superconducting transition.

[1] A.A. Zyuzin and A.Yu. Zyuzin, Phys. Rev. B 79, 174514 (2009).

62

conference program · 2009. 12. 23. · conference program thursday, june 11 morning 8:55 – 9:00...

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