Experiments withsemifluxon generator

Edward GoldobinUniversity of Tübingen, Germany

M. Paramonov, M. Fominsky, V. KosheletsIRE RAS, Moscow

[Logo of МОН 1.5 here]

Where is Tübingen?

Tübingen

Tübingen:• small university town on r. Neckar• population ~80000• 30 km south from Stuttgart

-- a capital of Baden-Württemberg

University:• students ~28000• university is 530 years old !!!• two faculties of theology ;-)• strong medicine• phys., chem., math are small

Our Group (~30 people):• 2 Profs: R. Kleiner, D. Koelle• 1 Assistant Prof.• 4 Post Docs• ~12 PhD students• ~10 Diploma students

Josephson junction

Conventional JJ. (0-junction)

Unconventional JJ (-junction)SIS

SIS

I

I

+other terms

jc=1–5000 A/cm2, (Nb-AlOx-Nb)0 1 2 3 4 5 6

-1.0

-0.5

0.0

0.5

1.0

sup

erc

urr

en

t

phase

11

is en

22

is en

12 :phase Josephson

11

is en

22

is en

Long Josephson 0- junction

0 x

1D model

YBCO-Nb ramp zigzags

H.-J. Smilde at al. PRL 88, 57004 (2002)

LTSEM image of supercurrent

E. Goldobin, R. Straub, D. Dönitz,D. Koelle, R. Kleiner,H. Hilgenkamp (2003).

SFS/SIFS junctions

V. Ryazanov et al. PRL 86, 2427 (2001)

T. Kontos et al. PRL 89, 137007 (2002)

sine-Gordon equation for 0- LJJ

Phase discontinuity points!

Goldobin et al., PRB 66, 100508 (2002)

— dimensionless damping

— the first critical field

— dimensionless field

Semifluxon=vortex carrying

-3 -2 -1 0 1 2 3 -3 -2 -1 0 1 2 3

0.0

0.5

1.0

1.5

2.0

-3 -2 -1 0 1 2 3

-1.0

-0.5

0.0

0.5

1.0

fluxo

n

(x)

2

2

coordinate x

phas

e

(x) (a)

coordinate x

2

x(x)

mag

netic

fie

ld

(b)

fluxon

sem

i-flu

xon

semi-fluxon

fluxo

n

coordinate x

supe

rcur

rent

(c)

Pinned, two degenerate states and

Goldobin et al., PRB 66, 100508 (2002)

Xu et al., PRB 51, 11958 (1995)

Mechanical analog:pendula chain

(x)

(x)

Semifluxons observation

SQUID microscopy on YBCO-Nb ramp zigzag LJJs

H. Hilgenkamp et al. Nature 422, 50 (2003).

Artificial 0- junctions

Goldobin et al., Phys. Rev. Lett. 92, 057005 (2002)

A. Ustinov, Appl. Phys. Lett. 80, 3153 (2000).

Nb LJJ with two injectors

J 30 m (jc 100 A/cm2)

Calibration of injectors

Numerical Experimental

-2 - 0 + +20.0

0.2

0.4

0.6

0.8

1.0

criti

cal c

urre

nt c

phase discontinuity -40 -30 -20 -10 0 10 20 30 40

0.00

0.05

0.10

0.15

0.20

0.25

0.30

I inj =

+0.

3 m

A

I inj =

+13

.5 m

A

criti

cal c

urre

nt I

c (m

A)

current through injectors Iinj (mA)

I inj =

–12

.8 m

A

Goldobin et al., PRL 92, 057005 (2004)

Switching on the current...

at zero bias we have a static pinned semifluxon. bias current pulls semifluxons, just like fluxons. but semifluxons are pinned --> deformation at bias=Ic0.64 Ic switching to the R-state

Goldobin et al., PRB 67, 224515 (2003).

mag

netic

fie

ld

Overcritical bias:oscillator

Frequency depends on: bias current, damping, length two outputs shifted by 180° more stable than flux-flow due

to semifluxon pinning

volta

ge

0.0

0.5

1.0

1.5

2.0

0 1 2 3 4 5 6 7

L=40J

L=20J

L=10J

normalized voltage u

bias

cur

rent

N. Lazarides, PRB 69, 212501 (2004).

-3 -2 -1 0 1 2 3

-1

0

1

coordinate x

mag

netic

fie

ld (

a.u.

)

Semifluxon -- half-integer ZFS

Finite length --> image technique: 1 real semifluxon + 2 anti-semifluxons (images)

Bias current Force SF hopping.

Goldobin et al., Phys. Rev. B 67, 224515 (2003).

Half integer ZFS (full IVC)

0,0 0,5 1,0 1,5 2,0 2,5 3,0

0,0

0,1

0,2

0,3

0,4

0,5

semi-integer ZFS

bi

as c

urre

nt,

mA

voltage across LJJ, mV

integer ZFS

Goldobin et al., PRL 92, 057005 (2004)

Half integer ZFS

0 100 200 300 400

0

20

40

60

80

sem

i-in

tege

r Z

FS

bias

cur

rent

(A

)

voltage across LJJ (V)

inte

ger

ZF

S

resonantstructures

Im

Goldobin et al., PRL 92, 057005 (2004)

Experiments last week in IRE

Layout

L = 16..32 mdx=dw=1, 1.5, 2 m

Calibration: Ic(ICL) & Ic(Iinj)

I-V characteristic of generator

SIS detector

Emission linesDifferent bias points along the semifluxon step

Autonomous linewidth ~1.2 … 10 MHz

And now with PLL ;-)

with PLL the spectral ratio is up to 97%

Summary & ProblemsSummary many samples work (both generator and detector) we observe expected operation: a semifluxon step, SIS pumping we have measured autonomous linewidth ..and linewidth with PLL

Outlook (problems & todos): maximum Ic in Ic(H) and Ic(Iinj) are not equal

in high freq. setup strange shunt resistance of ~3 Ohm in high freq. setup strange dep. of voltale on Iinj.

Repeat again with remaining 2 samples and try to make new ones. Compare linewidth with inj with the one with CL. Compare with ZFS not all LO freq were good