Diapositive 1

1
Schegolev Memorial Conference 2009
STM on highly disordered superconducting films
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.
Feigelman, L. D. Landau Institute for
Theoretical Physics - Moscow
2
Schegolev Memorial Conference 2009
Outline

• The superconductor-insulator transition
• Spectroscopy at 50 mK in TiN films
• Spectroscopy above Tc in TiN films
• Spectroscopy below and above Tc in a-InO films
• Conclusions

3
Titanium nitride thin filmsd 5 nm
SIT
Continuous decrease of Tc with increasing disorder
I1 T0 0.25 K I2 T0 0.38 K I3 T0 0.61 K
Activated behavior superconductivity related ?
T. I. Baturina, A Yu Mironov, V. M. Vinokur, M.
R. Baklanov and C. Strunk PRL 99, 257003 (2007)
4
SIT
Magneto-resistance peak
Magneto-resistance peak superconductivity
related ?
T. I. Baturina, C. Strunk, M. R. Baklanov, and A.
Satta PRL 98, 127003 (2007)
5
SIT
Indium oxide thin filmsd 20 nm - 200 nm
V. F. Gantmakher et al., JETP 82, 951 (1996)
Activation energy T0 converges towards Tc
D. Shahar and Z. Ovadyahu, Phys. Rev. B 46,
10917, (1992)
6
Schegolev Memorial Conference 2009
Outline

• The superconductor-insulator transition
• Spectroscopy at 50 mK in TiN films
• Spectroscopy above Tc in TiN films
• Spectroscopy below and above Tc in a-InO films
• Conclusions

7
Tunneling spectroscopy at 50 mK in TiN
Transport and tunneling spectroscopy
Sacépé et al. PRL 101, 157006 (2008)
Tc K ?/Tc
4.7 1.8
1.3 2.3
1 2.6
0.45 4
Increasing disorder
8
Tunneling spectroscopy at 50 mK in TiN
A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev.
Lett. 81, 3940, (1998) - Phys. Rev. B 65, 014501
(2001)
Tc K ?/Tc
4.7 1.8
1.3 2.3
1 2.6
0.45 4
9
Tunneling spectroscopy at 50 mK in TiN
Tunneling spectroscopy at 50 mK in TiN
Inhomogeneous superconducting state
M. Ma and P.A. Lee, Phys. Rev. B 32, 5658, (1985)
A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev.
Lett. 81, 3940, (1998) Phys. Rev. B 65, 014501
(2001)
10
Tunneling spectroscopy at 50 mK in TiN
Coulomb suppression and mesoscopic fluctuations
of Tc
A. M. Finkelstein, Pissma Zh. Eksp. Theor. Fiz.,
45, 46 (1987)
M. A. Skvortsov and M. V. Feigelman, Phys. Rev.
Lett. 95, 057002, (2005)
11
Tunneling spectroscopy at 50 mK in TiN
Inhomogeneous superconducting state
TiN 1 (Tc 1.3 K)
?(r)
Tc K ?/Tc Var.
4.7 1.8 ---
1.3 2.3 12
1 2.6 20
0.45 4 50
A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev.
Lett. 81, 3940, (1998)
B. Sacépé, et al. Phys. Rev. Lett. 101, 157006,
(2008)
11
12
Tunneling spectroscopy at 50 mK in TiN
Tunneling spectroscopy at Low temperatureSummary
Activated behavior
A. M. Finkelstein, Pissma Zh. Eksp. Theor. Fiz.,
45, 46 (1987)
13
Schegolev Memorial Conference 2009
Outline

• The superconductor-insulator transition
• Spectroscopy at 50 mK in TiN films
• Spectroscopy above Tc in TiN films
• Spectroscopy below and above Tc in a-InO films
• Conclusions

14
Tunneling spectroscopy above Tc in TiN
Temperature evolution of the tunneling conductance
TiN 2 Tc 1 K (close to the SIT)
TiN bulk Tc 4.7 K (far from the SIT)
Superconducting fluctuations
W. Escoffier, et al., Phys. Rev. Lett. 93,
217005, (2004)
14
15
Tunneling spectroscopy above Tc in TiN
16
Tunneling spectroscopy above Tc in TiN
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Tunneling spectroscopy above Tc in TiN
One parameter fit Tc
Tc K
1.3
1
0.45
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Tunneling spectroscopy above Tc in TiN
Superconducting fluctuations correction to the DOS
A. Varlamov and V. Dorin, Sov. Phys. JETP 57,
1089, (1983)
R? kO Tc (R?) K Tc (DOS) K
3.5 1.3 1.27
4.3 1.0 0.98
7.4 0.45 0.45
Slopes increase with Gi R? Valid up to e gt 1
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Tunneling spectroscopy above Tc in TiN
Superconducting fluctuations correction to the DOS
A. Varlamov and V. Dorin, Sov. Phys. JETP 57,
1089, (1983)
R? kO Tc (R?) K Tc (DOS) K
3.5 1.3 1.27
4.3 1.0 0.98
7.4 0.45 0.45
Striking sensitivity to Tc
20
Schegolev Memorial Conference 2009
Outline

• The superconductor-insulator transition
• Spectroscopy at 50 mK in TiN films
• Spectroscopy above Tc in TiN films
• Spectroscopy below and above Tc in a-InO films
• Conclusions

21
Tunneling spectroscopy in InO
Indium oxide thin filmsd 15 -35 nm
Spectra measured at different locations
Strong inhomogeneities
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Tunneling spectroscopy in InO
Indium oxide thin filmsd 15 -35 nm
Spectra measured at different locations
Strong inhomogeneities
23
Tunneling spectroscopy at 50 mK in TiN
Inhomogeneous superconducting state
M. Ma and P.A. Lee, Phys. Rev. B 32, 5658, (1985)
A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev.
Lett. 81, 3940, (1998) Phys. Rev. B 65, 014501
(2001)
24
Tunneling spectroscopy in InO
Superconducting gap
 Insulating  gap
A. Ghosal, M. Randeria, N. Trivedi, Phys. Rev.
Lett. 81, 3940, (1998) Phys. Rev. B 65, 014501
(2001)
25
Tunneling spectroscopy in InO
Proliferation of spectra without coherence peaks
when approaching the insulating state
26
Tunneling spectroscopy in InO
Pseudogaps without coherence peaks signature of
localized Cooper pairs see M. Feigelman talk
(this session)
T(peak) Tc for any local gap amplitude
27
Conclusions
Superconducting inhomogeneous state with
non-zero gap at the SIT at T0
Pseudogap state above Tc described by the
superconducting fluctuations
Localization of Cooper pairs