B. Sacépé, T. Dubouchet, C. Chapelier, M. Sanquer, CEA - Grenoble

T. Baturina, Institute of semiconductor Physics - Novosibirsk

V. Vinokur, Material Science Division, Argonne National Laboratory - Argonne

M. Baklanov, A Satta, IMEC - Leuven

M. Ovadia, D. Shahar, Weizmann Institute of Science - Rehovot

M. Feigel’man, L. D. Landau Institute for Theoretical Physics - Moscow

Schegolev Memorial Conference 2009

STM on highly disordered superconducting films

Outline

• The superconductor-insulator transitionThe superconductor-insulator transition•Spectroscopy at 50 mK in TiN filmsSpectroscopy at 50 mK in TiN films•Spectroscopy above Tc in TiN filmsSpectroscopy above Tc in TiN films•SpectroscopySpectroscopy below and above Tc in a-InO a-InO filmsfilms•ConclusionsConclusions

Schegolev Memorial Conference 2009

1/T [K]

Titanium nitride thin filmsTitanium nitride thin filmsd = 5 nmd = 5 nm

T. I. Baturina, A Yu Mironov, V. M. Vinokur, M. R. Baklanov and C. Strunk

PRL 99, 257003 (2007)

Continuous decrease of Tc with increasing disorder

Activated behavior : superconductivity related ?

I1 : T0 = 0.25 K

I2 : T0 = 0.38 K

I3 : T0 = 0.61 K

SIT

Magneto-resistance peak

T. I. Baturina, C. Strunk, M. R. Baklanov, and A. Satta

PRL 98, 127003 (2007)

Magneto-resistance peak : superconductivity related ?

SIT

V. F. Gantmakher et al., JETP 82, 951 (1996)

D. Shahar and Z. Ovadyahu, Phys. Rev. B 46, 10917, (1992)

Indium oxide thin filmsIndium oxide thin filmsd = 20 nm - 200 nmd = 20 nm - 200 nm

SIT

Activation energy T0 converges towards Tc

Outline

• The superconductor-insulator transitionThe superconductor-insulator transition•Spectroscopy at 50 mK in TiN filmsSpectroscopy at 50 mK in TiN films•Spectroscopy above Tc in TiN filmsSpectroscopy above Tc in TiN films•SpectroscopySpectroscopy below and above Tc in a-InO a-InO filmsfilms•ConclusionsConclusions

Schegolev Memorial Conference 2009

-1,0 -0,5 0,0 0,5 1,00,0

0,5

1,0

1,5

2,0

G(V

), no

rmal

ized

V [mV]

= 260 µeVTeff = 0,25 K

-1,0 -0,5 0,0 0,5 1,00,0

0,5

1,0

1,5

2,0

= 225 µeVTeff = 0,32 K

G(V

), no

rmal

ized

V [mV]

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,00

1

2

3

4

5

6

7

8

R

[k]

T [K]

TiN 1 TiN 2 TiN 3

Tc [K] Δ/Tc

4.7 1.81.3 2.31 2.6

0.45 4

-1,0 -0,5 0,0 0,5 1,00,0

0,5

1,0

1,5

2,0

= 154 µeVTeff = 0,35 K

G(V

), no

rmal

ized

V [mV]

Increasing disorder

Sacépé et al.PRL 101, 157006 (2008)

Tunneling spectroscopy at 50 mK in TiNTransport and tunneling spectroscopy

Tc [K] Δ/Tc

4.7 1.81.3 2.31 2.6

0.45 4

λ

λ

Increasing disorder

-1,0 -0,5 0,0 0,5 1,00,0

0,5

1,0

1,5

2,0

G(V

), no

rmal

ized

V [mV]

= 260 µeVTeff = 0,25 K

-1,0 -0,5 0,0 0,5 1,00,0

0,5

1,0

1,5

2,0

= 225 µeVTeff = 0,32 K

G(V

), no

rmal

ized

V [mV]-1,0 -0,5 0,0 0,5 1,0

0,0

0,5

1,0

1,5

2,0

= 154 µeVTeff = 0,35 K

G(V

), no

rmal

ized

V [mV]

A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev. Lett. 81, 3940, (1998) - Phys. Rev. B 65, 014501 (2001)

Tunneling spectroscopy at 50 mK in TiN

λ

Tunneling spectroscopy at 50 mK in TiN

Inhomogeneous superconducting state

A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev. Lett. 81, 3940, (1998)Phys. Rev. B 65, 014501 (2001)

M. Ma and P.A. Lee, Phys. Rev. B 32, 5658, (1985)

Tunneling spectroscopy at 50 mK in TiN

M. A. Skvortsov and M. V. Feigel’man, Phys. Rev. Lett. 95, 057002, (2005)

Coulomb suppression and mesoscopic fluctuations of Tc

A. M. Finkelstein, Pis’sma Zh. Eksp. Theor. Fiz., 45, 46 (1987)

Tunneling spectroscopy at 50 mK in TiN

TiN 1 (Tc = 1.3 K)

A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev. Lett. 81, 3940, (1998)

Δ(r)Tc [K] Δ/Tc

Var. [%]

4.7 1.8 ---

1.3 2.3 12

1 2.6 20

0.45 4 50

11

B. Sacépé, et al. Phys. Rev. Lett. 101, 157006, (2008)

Tunneling spectroscopy at 50 mK in TiN

Inhomogeneous superconducting state

Activated behavior

Tunneling spectroscopy at Low temperatureSummary

A. M. Finkelstein, Pis’sma Zh. Eksp. Theor. Fiz., 45, 46 (1987)

Tunneling spectroscopy at 50 mK in TiN

Outline

• The superconductor-insulator transitionThe superconductor-insulator transition•Spectroscopy at 50 mK in TiN filmsSpectroscopy at 50 mK in TiN films•Spectroscopy above Tc in TiN filmsSpectroscopy above Tc in TiN films•SpectroscopySpectroscopy below and above Tc in a-InO a-InO filmsfilms•ConclusionsConclusions

Schegolev Memorial Conference 2009

Superconducting fluctuations

TiN 2 – Tc = 1 K(close to the SIT)

TiN bulk – Tc = 4.7 K(far from the SIT)

14

Tunneling spectroscopy above Tc in TiN

Temperature evolution of the tunneling conductance

W. Escoffier, et al., Phys. Rev. Lett. 93, 217005, (2004)

Tunneling spectroscopy above Tc in TiN

Tunneling spectroscopy above Tc in TiN

Tc [K]

1.31

0.45

One parameter fit : Tc

Tunneling spectroscopy above Tc in TiN

Superconducting fluctuations correction to

the DOS

A. Varlamov and V. Dorin, Sov. Phys. JETP 57, 1089, (1983)

Slopes increase with Gi ~ R□

Valid up to ε > 1

R□

[kΩ]Tc (R□) [K]

Tc (DOS)

[K]

3.5 1.31.3 1.271.27

4.3 1.01.0 0.980.98

7.4 0.450.45 0.450.45 Validity :

Tunneling spectroscopy above Tc in TiN

Superconducting fluctuations correction to

the DOS

A. Varlamov and V. Dorin, Sov. Phys. JETP 57, 1089, (1983)

Striking sensitivity to Tc

R□

[kΩ]Tc (R□) [K]

Tc (DOS)

[K]

3.5 1.31.3 1.271.27

4.3 1.01.0 0.980.98

7.4 0.450.45 0.450.45

Tunneling spectroscopy above Tc in TiN

Outline

• The superconductor-insulator transitionThe superconductor-insulator transition•Spectroscopy at 50 mK in TiN filmsSpectroscopy at 50 mK in TiN films•Spectroscopy above Tc in TiN filmsSpectroscopy above Tc in TiN films•SpectroscopySpectroscopy below and above Tc in a-InO a-InO filmsfilms•ConclusionsConclusions

Schegolev Memorial Conference 2009

Strong inhomogeneities :Strong inhomogeneities :

Spectra measured at different locations

Tunneling spectroscopy in InO

Indium oxide thin filmsIndium oxide thin filmsd = 15 -35 nmd = 15 -35 nm

Strong inhomogeneities :Strong inhomogeneities :

Spectra measured at different locations

Tunneling spectroscopy in InO

Indium oxide thin filmsIndium oxide thin filmsd = 15 -35 nmd = 15 -35 nm

λ λ

Inhomogeneous superconducting state

A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev. Lett. 81, 3940, (1998)Phys. Rev. B 65, 014501 (2001)

M. Ma and P.A. Lee, Phys. Rev. B 32, 5658, (1985)

Tunneling spectroscopy at 50 mK in TiN

λ

« Insulating » gap

Superconducting gap

A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev. Lett. 81, 3940, (1998)Phys. Rev. B 65, 014501 (2001)

Tunneling spectroscopy in InO

Tunneling spectroscopy in InO

Proliferation of spectra without coherence peaks when approaching the insulating state

Tunneling spectroscopy in InO

Pseudogaps without coherence peaks : signature of localized Cooper pairssee M. Feigel’man talk (this session)

T(peak) = Tc for any local gap amplitude

non-zero gap at the SIT at T=0

Pseudogap state above Tc described by the superconducting fluctuations

Conclusions

Superconducting inhomogeneous state with

Localization of Cooper pairs