Weizmann October2008

8/13/2019 Weizmann October2008

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Disorder and magnetic field tunedinsulating state in a-InO

superconducting films

1Department of Condensed Matter Physics, Weizmann Institute of Science

2Department of Condensed Matter Physics, Geneva University

Benjamin Sacp1,2, Maoz Ovadia1, Dan Shahar1


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Outline

1. Introduction

2. Linear transport

3. Non-linear transport

4. Electron overheating


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Outline

1. Introduction

2. Linear transport




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1/T [K]

Disorder-drivenSuperconductor-Insulator Transition

0exp T

RT

I1 : T0= 0.25 K

I2 : T0= 0.38 K

I3 : T0 = 0.61 K

Titanium nitride thin filmsd 5 nm

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

PRL 98, 127003 (2007)


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

Disorder-drivenSuperconductor-Insulator Transition

Amorphous Indium Oxyde

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


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Magnetic field-tuned SIT

TiNInOx

G. Sambandamurthy, L.W. Engel, A. Johansson, E.

Peled, D. Shahar, PRL 94, 017003, (2005)

T. Baturina, C. Strunk, M. Baklanov,A. Satta,PRL 98, 127003, (2007)


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Magnetic field-tuned SIT

Activated regime 10( ) exp T

R T RT

G. Sambandamurthy, L.W. Engel, A. Johansson, D.

Shahar,PRL 92, 107005, (2004)


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Collective insulating state



Magnetic field-tuned insulating stateInOx


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Collective insulating state



T. Baturina, A. Mironov, V. Vinokur, M. Baklanov,

C. Strunk,PRL 99, 257003, (2007)

Magnetic field-tuned insulating stateInOxDisorder-tuned insulating stateTiN

Strong instability occurs around T* ~ 0.1KZero conductive state ?


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Superconductor-Insulator Transition (SIT)

Alternative answer :Joule overheating of electrons

(B. Altshuler, V. Kravtsov, I. Lerner, I. Aleiner, cond-mat/0810.4312)

Question :

Origin of this instability in the I-V curves

New phase transition at T*~0.1K ?

Superinsulating state ?


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Outline

1. Introduction

2. Linear-transport




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R(T)

InO-I : Thickness = 30 nm, R(300K) ~ 2 k/

InO-S: same sample after 4 days of annealing at 300K

InO-I

InO-S

Amorphous Indium Oxide


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Magnetoresistance(2 probes measurements)

InO-I InO-S


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Activated regime under magnetic field ?

InO-I

(note: perpendicular field)

Before the MR peak:Over-activation ?

After the MR peak:Sub-activation ?


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InO-S

Activated regime only around the magnetoresistance peak !

Activated regime under magnetic field ?


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Outline

1. Introduction

2. Linear transport

3. Non-linear transport B-dependence of voltage threshold Low current branch



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I(V) curves at B=0T

InO-I


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I(V) curves at B=8T

InO-I

VTchanges by 3 orders of magnitude !


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I(V) curves at B=12T

InO-I T* < 30mK

T* decrease at high field


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I(V) curves InO-S

InO-S


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B-dependence of the voltage threshold

VT(B=0) = 2 mV

InO-SInO-I


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T cV B B

VTchanges by 4 orders of magnitude

VTfollows a power law with B

2.1

0.8



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VTchanges by 4 orders of magnitude

VTfollows a power law with B

2.1

0.8


Length scale L behind VT?

eEL T

16 1.2

2 10

T

T

nm for V V L

mm for V V

Answer : no !


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Outline

1. Introduction

2. Linear transport

3. Non-linear transport B-dependence of voltage threshold Low current branch



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Current below VT?

InO-I


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Current below VT?

InO-I InO-S


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Low-current branch

I-V is linear at low voltage !

InO-S


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I-V is exponential at higher bias

Low-current branch


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Extrapolation of the linear resistance

Possible fit :

linear for V


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Possible fit :

linear for V


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00

exp 1V

I V IV



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Extrapolation of R(T)

Sub-activation seems confirmed at high field

InO-S


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Superinsulator ?

Question: is there a superinsulator state in InOx ?

Answer: No !


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Current jump in YxSi1-x

Activated regime(T0~ 0.5K)for both thin (40nm) and thick(7m) films

Absence of superconductingcorrelations


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Outline

1. Introduction

2. Linear-transport




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Overheating of electrons

cond-mat / 0810.4312

2

6 6

( ) el ph

el

Vc T T A

R T

Heat balance equation (dirty metal) :

0

0

( ) expR T RT

Insulating behaviour :


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Overheating of electrons

cond-mat / 0810.4312

2

6 6

( ) el ph

el

Vc T T

R T

Heat balance equation (dirty metal) :


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Electronic temperature

B. Altshuler et al.

cond-mat / 0810.4312


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( , ) ( , )ph phdI

G V T V T dV

1( ) ( 0, )ph ph elR T G V T T

( , )el phT V T

B. Altshuler et al.

cond-mat / 0810.4312


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( , )el ph

T V T

B. Altshuler et al.

cond-mat / 0810.4312


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Electron overheating

2

2 6 6( , )

( ) ph el ph

el

VV G V T c T T

R T Heat balance equation :

[W]


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2

2 6 6( , )

( ) ph el ph

el

VV G V T c T T


[W]


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Summary

Voltage threshold : changes by 4 orders of magnitude

follows a power law with field

Low-current branch : Linear at low bias

Exponential at higher bias

give an extrapolation of R(T)

Electron overheating : Give an alternative description

Justify the extrapolation of R(T) from the I-V cuvres


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Thank you for your attention


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2

2 6 6( , )

( ) ph el ph

el

VV G V T c T T


C =.V => = 1 nW/m3/K6

( In a metal : ~ 1 nW/m3/K5 )

Application: heating Tel= 90mK and Tph=20mK

Metal P=V2/R ~ 6e-7 nW/m3

Dirty metal P=V2/R ~ 5e-6 nW/m3


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Extrapolation of R(T)

InO-SActivated ? Efros-Shklovskii ?


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Four probes measurments

Anisotropy


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Anisotropy

Perpendicular Field

Parallel Field

B dependence of the voltage


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B-dependence of the voltagethreshold

Fluctuations of VTstop at the maximum of VT(B)


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2

2 6 6( , )

( ) ph el ph

el

V V G V T c T T R T

Heat balance equation :


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I(V) curves at B=12T

InO-I T* < 30mK

T* decrease at high field

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Weizmann October2008