Quantum Transport in InAs/GaSb Wei Pan Sandia National Laboratories - - PowerPoint PPT Presentation

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Quantum Transport in InAs/GaSb Wei Pan Sandia National Laboratories - - PowerPoint PPT Presentation

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Quantum Transport in InAs/GaSb Wei Pan Sandia National Laboratories Albuquerque, New Mexico, USA Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin

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SLIDE 1

Quantum Transport in InAs/GaSb

Wei Pan

Sandia National Laboratories Albuquerque, New Mexico, USA

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department

  • f Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
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SLIDE 2

Outline

  • InAs/GaSb heterostructure
  • The experiments and results

– Circular conductivity law in the charge neutrality regime in an InAs/GaSb field-effect-transistor – McMillan-Rowell like oscillations in a Ta-InAs/GaSb-Ta junction – Giant supercurrent in a Ta-InAs/GaSb-Ta junction

  • Summary
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SLIDE 3

InAs/GaSb heterostructure:

Eg0

D

Quantum spin Hall effect

C.X. Liu, T.L. Hughes, X.L. Qi, K. Wang, and S.C. Zhang, Phys. Rev. Lett. 100, 236601 (2008).

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SLIDE 4

Outline

  • InAs/GaSb heterostructure
  • The experiment and results

– Circular conductivity law in the charge neutrality regime in an InAs/GaSb field-effect-transistor

– McMillan-Rowell like oscillations in a Ta-InAs/GaSb-Ta junction – Giant supercurrent in a Ta-InAs/GaSb-Ta junction

  • Summary
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SLIDE 5

air

  • InAs 20A (or GaSb 20A)
  • AlSb 500A
  • GaSb QW 50A
  • InAs QW 150A
  • AlSb 1um
  • GaSb 1um
  • GaSb substrate (p-doped)

Growth structure:

GaSb buffer on p-type GaSb

AlSb

Field-effect transistor:

Yang et al, Appl. Phys. Lett. 69, 85 (1996).

Eg0

D

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SLIDE 6

I

Rxx Rxy

Vg

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SLIDE 7

Electron transport at zero magnetic field:

  • 10
  • 5

5 10 2 4 6

Rxx (k)

Vg (V)

B = 0 T T ~ 25 mK

Eg0

D

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SLIDE 8
  • 3.5
  • 3.0
  • 2.5
  • 2.0
  • 1.5
  • 1.0

5 10 15

Gxx (e

2/h)

Vg (V) T ~ 25 mK B = 0 T 4e

2/h

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SLIDE 9

Eg0

D

sth

xx  e2/h  Eg0/D

Eg0 ~ 15 meV D ~ 1 meV sth

xx  15 e2/h

Gth

xx = 5 e2/h ~ 4 e2/h

  • Y. Naveh and B. Laikhtman, Europhys. Lett. 55, 545 (2001).
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SLIDE 10

Gxx = 3.97 + 0.10log (T)

L.J. Cooper et al, Phys. Rev. B 57 11915 (1998)

10 100 1000 4.1 4.2 4.3

T (mK) Gxx (e

2/h)

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SLIDE 11

Electron transport at low magnetic fields:

2 3 4 5 6 7 8 9 10 0.00 0.02 0.04

Rxx (arb. units) Vg (T) 22 34 28 =16 B = 2 T

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SLIDE 12

At charge neutrality point CNP (n + p =0) |n| = |p| ~ 0.61011 cm-2

  • 10
  • 5

5 10

  • 10
  • 5

5 10 15

n, p (10

11 cm

  • 2)

Vg (V)

n=3.93+1.35xVg p=2.65+1.31xVg

CNP

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SLIDE 13
  • 6
  • 3

3 6

  • 4

4 8 12

2 1

Vg (V) sxx, sxy (e

2/h)

sxx sxy

B = 5T

4 56

e=12 h=-2

  • 4
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SLIDE 14

Electron transport at high magnetic fields:

  • 10
  • 5

5 10

  • 2

2 4

1

sxx & sxy (e

2/h)

Vg (V)

B = 20 T T ~ 30 mK

e=3

2

h

  • 1
  • 2
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SLIDE 15

(sxx – N)2 + sxy

2 = N2

  • 4
  • 3
  • 2
  • 1

1 2 3 4 1 2 3 4 5 6 7 8

sxx (e

2/h)

sxy (e

2/h)

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SLIDE 16

Semi-Circular conductivity law in quantum Hall plateau transition

  • M. Hilke et al, Nature (1998)

(sxy – /2)2 + sxx

2 = (/2)2

independently of rxx

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SLIDE 17

(sxx – N)2 + sxy

2 = N2

rxx = h/e2/(2N)

  • 10
  • 5

5 10

  • 1.0
  • 0.5

0.0 0.5 1.0

  • 2

B = 20 T T ~ 30 mK

rxx & rxy (h/e

2)

Vg (V)

3 2

e=1 h=-1

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SLIDE 18

The circular conductivity law due to co-existence of both electrons and holes and their interactions

  • In the CN regime, electron density and hole density low.
  • Landau level filling factors for electrons and holes small
  • Without e-h interactions, 2D electrons and holes in high

magnetic field induced insulating phase, sxx =0 and sxy = 0.

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SLIDE 19
  • Breakup of perfect dissipationless edge states due to disorder

and e-h interactions.

  • Breakup of stable orbits can give rise to chaotic motions.

[G. Müller, G.S. Boebinger et al, Phys. Rev. Lett. 75, 2875 (1995).] R.J. Nicolas et al, Phys. Rev. Lett. 85, 2364 (2000)

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SLIDE 20

Outline

  • InAs/GaSb heterostructure
  • The experiment and results

– Circular conductivity law in the charge neutrality regime in an InAs/GaSb field-effect-transistor

– McMillan-Rowell like oscillations in a Ta-InAs/GaSb-Ta junction – Giant supercurrent in a Ta-InAs/GaSb-Ta junction

  • Summary
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SLIDE 21
  • K. Chang, unpublished
  • Z. Liu et al., Acta Phys. Sin. 2012, 61, 217303

8-band k.p calculations with QW widths (GaSb 5 nm; InAs 10 nm)

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SLIDE 22

Density n = 1.8x1011 cm-2 Mobility m = 1.2x105 cm2/Vs EF = 18.7 meV lmfp = 0.8 mm VF = 5.4x105 m/s

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SLIDE 23

S-N-S junction

Ta-InAs/GaSb-Ta junction

InAs 2 nm Ta 240 nm Ta 240 nm

AlSb 50 nm GaSb 5 nm InAs 10 nm AlSb 50 nm

  • Junction: W=10 mm L= 2 mm

I V

Ta Ta

bilayer

10 20 30 40

50 100 150 200

R ()

T (K)

Tc=1.55K

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SLIDE 24

Zero bias conductance peak + multiple equally spaced dips IDC+dI VDC+dV

Ta Ta

  • 40
  • 20

20 40 50 100 150 200 250

dI/dV (e

2/h)

DCV on sample (mV) T=0.5 K B=0

VDC (meV)

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SLIDE 25

McMillan-Rowell Oscillations (MRO)

  • J. M. Rowell and W. L. McMillan, Phys. Rev. Lett. 16, 453 (1966).
  • C. Visanli et al, Nature Physics 8, 539 (2012).
  • B. Wu et al, arXiv:1305.5140.

Vn = V0 + n×hVF/4dN

N S

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SLIDE 26

McMillan-Rowell like Oscillations

Vn = V0 + n×hVF/4dN

  • 40
  • 20

20 40 50 100 150 200 250

dI/dV (e

2/h)

DCV on sample (mV) T=0.5 K B=0

n=12 3 4

  • 40
  • 20

20 40 50 100 150 200 250

dI/dV (e

2/h)

DCV on sample (mV) T=0.5 K B=0

n=12 3 4

1 2 3 4 5 10 20 30 0.5 K 0.3 K Vn (mV)

n

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SLIDE 27

One serious issue with MRO explanation: From the slope of MRO plot, a Fermi velocity of VF = 1.3x107 m/s is obtained. This value is much larger than that (VF= 5.4x105 m/s)

  • btained fro SdH oscillations.
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SLIDE 28

Giant super-current in Ta- InAs/GaSb-Ta junction

I V

Ta Ta

bilayer

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SLIDE 29

Giant super-current observed

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SLIDE 30

Large Tc

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SLIDE 31

I (mA)

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SLIDE 32
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SLIDE 33

A couple of details:

1) Very large Jc, Jc = 350 nA/mm >> ~15 nA/mm reported by

  • ther groups.

(considering L = 2mm, xsc ~ 80nm (bulk Ta) and lmfl = 0.8mm)

2) Large number of flux per lobe ~ 300 F0 >>1. A large value of flux per lobe was also observed in S-GaAs- S junction by Rokhinson et al.

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SLIDE 34

Summary:

(1) Well-developed integer quantum Hall effect states at Landau level fillings =1, 2 in the hole regime and =1, 2, 3… in the electron regime. (2) Chaotic quantum transport behavior at extremely high magnetic fields around the charge neutrality point. (3) Circular conductivity law in sxx versus sxy. (4) MRO in Ta-InAs/GaSb-Ta junction device (5) Giant supercurrent in Ta-InAs/GaSb-Ta junction

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SLIDE 35

Collaborators:

Sandia:

– John Klem – Sam Hawkins – Ken Lyo – Jin Kim – Mike Cich – Madhu Thalakulam – Wenlong Yu – Xiaoyan Shi

Princeton:

– Jian Li – Andrei Berniverg

Georgia Tech:

– Wenlong Yu – Zhigang Jiang

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SLIDE 36