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