Quantum Transport in InAs/GaSb

Transcription

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 of Energy s National Nuclear Security Administration under contract DE-AC04-94AL85000.

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

3 InAs/GaSb heterostructure: E g0 D Quantum spin Hall effect C.X. Liu, T.L. Hughes, X.L. Qi, K. Wang, and S.C. Zhang, Phys. Rev. Lett. 100, (2008).

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

5 Growth structure: air InAs 20A (or GaSb 20A) AlSb 500A GaSb QW 50A InAs QW 150A AlSb 1um GaSb 1um GaSb substrate (p-doped) Field-effect transistor: Yang et al, Appl. Phys. Lett. 69, 85 (1996). AlSb GaSb buffer on p-type GaSb E g0 D

6 R xy R xx V g I

7 Electron transport at zero magnetic field: 6 B = 0 T T ~ 25 mk D E g0 R xx (k ) V g (V)

8 15 T ~ 25 mk B = 0 T G xx (e 2 /h) e 2 /h V g (V)

9 s th xx e 2 /h E g0 /D Y. Naveh and B. Laikhtman, Europhys. Lett. 55, 545 (2001). E g0 ~ 15 mev E g0 D D ~ 1 mev s th xx 15 e 2 /h G th xx = 5 e 2 /h ~ 4 e 2 /h

10 4.3 G xx = log (T) G xx (e 2 /h) L.J. Cooper et al, Phys. Rev. B (1998) T (mk)

11 Electron transport at low magnetic fields: 0.04 B = 2 T =16 R xx (arb. units) V g (T)

12 n, p (10 11 cm -2 ) n= xv g CNP -10 p= xv g V g (V) At charge neutrality point CNP (n + p =0) n = p ~ cm -2

13 12 B = 5T s xy s xx, s xy (e 2 /h) s xx e =12-4 h = V g (V)

14 Electron transport at high magnetic fields: 4 e =3 s xx & s xy (e 2 /h) h V g (V) 2 B = 20 T T ~ 30 mk

15 8 7 6 s xx (e 2 /h) s xy (e 2 /h) (s xx N) 2 + s xy2 = N 2

16 Semi-Circular conductivity law in quantum Hall plateau transition (s xy /2) 2 + s xx2 = ( /2) 2 independently of r xx M. Hilke et al, Nature (1998)

17 (s xx N) 2 + s xy2 = N 2 r xx = h/e 2 /(2N) e =1 2 3 r xx & r xy (h/e 2 ) h =-1 B = 20 T T ~ 30 mk V g (V)

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, s xx =0 and s xy = 0.

19 R.J. Nicolas et al, Phys. Rev. Lett. 85, 2364 (2000) 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).]

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

21 8-band k.p calculations with QW widths (GaSb 5 nm; InAs 10 nm) K. Chang, unpublished Z. Liu et al., Acta Phys. Sin. 2012, 61,

22 Density n = 1.8x10 11 cm -2 Mobility m = 1.2x10 5 cm 2 /Vs E F = 18.7 mev l mfp = 0.8 mm V F = 5.4x10 5 m/s

23 S-N-S junction InAs 2 nm Ta 240 nm AlSb 50 nm GaSb 5 nm Ta 240 nm Ta-InAs/GaSb-Ta junction Junction: W=10 mm L= 2 mm InAs 10 nm AlSb 50 nm bilayer 200 I Ta Ta V R ( ) T c =1.55K T (K)

24 Ta I DC +di Ta V DC +dv T=0.5 K B=0 di/dv (e 2 /h) DCV on sample (mv) V DC (mev) Zero bias conductance peak + multiple equally spaced dips

25 McMillan-Rowell Oscillations (MRO) V n = V 0 + n hv F /4d N S N 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:

26 McMillan-Rowell like Oscillations T=0.5 K B=0 30 di/dv (e 2 /h) n= DCV on sample (mv) 4 Vn (mv) K 0.3 K n V n = V 0 + n hv F /4d N

27 One serious issue with MRO explanation: From the slope of MRO plot, a Fermi velocity of V F = 1.3x10 7 m/s is obtained. This value is much larger than that (V F = 5.4x10 5 m/s) obtained fro SdH oscillations.

28 Giant super-current in Ta- InAs/GaSb-Ta junction bilayer Ta I Ta V

29 Giant super-current observed

30 Large Tc

31 I (ma)

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33 A couple of details: 1) Very large Jc, Jc = 350 na/mm >> ~15 na/mm reported by other groups. (considering L = 2mm, x sc ~ 80nm (bulk Ta) and l mfl = 0.8mm) 2) Large number of flux per lobe ~ 300 F 0 >>1. A large value of flux per lobe was also observed in S-GaAs- S junction by Rokhinson et al.

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 s xx versus s xy. (4) MRO in Ta-InAs/GaSb-Ta junction device (5) Giant supercurrent in Ta-InAs/GaSb-Ta junction

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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