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Spin-orbit interaction in a dual gated InAs/GaSb quantum well

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Presentation on theme: "Spin-orbit interaction in a dual gated InAs/GaSb quantum well"โ€” Presentation transcript:

1 Spin-orbit interaction in a dual gated InAs/GaSb quantum well
A. Beukman et al. (Kouwenhoven Group) arXiv: Logo of PASPS9 conference Kris Cerveny Friday Group Meeting Talk

2 Introduction Motivation: Experiment: InAs and GaSb have strong SOI
Rashba strength tunable with gating for InAs Control of SOI necessary for spintronic devices Strong SOI + large g-factor + inducible superconductivity ingredients for topological superconducting phase Experiment: Investigates SOI in dual-gated InAs/GaSb quantum well Tune between single and double carrier regimes ( ๐‘’ โˆ’ and ๐‘’ โˆ’ + holes) Analyze difference in density of SO split bands Extract zero-field density difference โˆ† ๐‘› ๐‘๐น SOI near hybridization gap

3 InAs/GaSb DQW InAs + GaSb ๏ƒจ Interesting band structure [1]
GaSb valence band maximum higher in energy than InAs conduction band minimum [2] Energy range where ๐‘’ โˆ’ in InAs coexist with holes from the GaSb Strong coupling ๏ƒจ ๐‘’ โˆ’ -hole hybridization ๏ƒจ gap when ๐‘› ๐‘’ โˆ’ โ‰ˆ ๐‘› โ„Ž [1] F. Qu et al., PRL 115, (2015) [2] H. Kroemer, Physica E 20 (2004)

4 Sample 20ฮผm x 80ฮผm Hall bar 300mK Measurements
GaSb substrate lattice matched with subsequent layers ๏ƒจ no need for thick buffer as with GaAs ๏ƒจ better coupling between BG and wells! [1] F. Qu et al., PRL 115, (2015)

5 ๐‘… ๐‘ฅ๐‘ฅ as function of ๐‘‰ ๐‘ก๐‘”/๐‘๐‘”
2T out of plane magnet High ๐‘… ๐‘ฅ๐‘ฅ (dashed lines) ๏ƒ  ๐ธ ๐น inside gap Green line separates single- and dual-carrier regimes Line ฮ™: ๐‘’ โˆ’ mobility highest Line ฮ™ฮ™: close to hybridization gap

6 Electron-only Regime Trace along line ฮ™ (fixed density)
Trends from 1-10: Extra frequency peak Asymmetry between beats (amplitude and oscillation #) Decreased spacing of peaks (decreasing โ–ณ ๐‘› ๐‘๐น ) Increasing # of oscillations in A & B ๏ƒ  nodes pushed to lower B fields Clear SdH oscillations in ๐‘… ๐‘ฅ๐‘ฅ ๏ƒ  beating pattern as function of ๐ต โŠฅ SdH osc. for each spin band periodic in 1 ๐ต ๐‘› ๐‘– = ๐‘’โˆ™ ๐‘“ ๐‘– โ„Ž System favors one SO eigenstate ๏ƒจ โ–ณ ๐‘› ๐‘๐น = ๐‘› 2 โˆ’ ๐‘› 1 ๏ƒจ โ–ณ ๐ธ ๐‘๐น๐‘†๐‘† =โ–ณ ๐‘› ๐‘๐น ( ๐‘š โˆ— ๐œ‹ โ„ 2 ) โˆ’1

7 Center Frequency Peak Emergent central peak does not correspond to a density 3 possible mechanisms can cause extra freq. components: Magnetic inter-subband scattering Magnetophonon resonances Magnetic breakdown: ๏ƒ  Carriers tunneling between spin polarized Fermi-surfaces Emergent central peak does not correspond to a density 3 possible mechanisms can cause extra freq. components: Magnetic inter-subband scattering Magnetophonon resonances Magnetic breakdown [Schematics] W. G. Chambers, Proc. Phys. Soc., Vol 84, 1964

8 Simulation vs Measurement
Parameter tuning yields: ๐›ผ 1 =75 ๐‘š๐‘’๐‘‰โ„ซ ๐›ฝ 1 =28.5 ๐‘š๐‘’๐‘‰โ„ซ ๐œธ ๐Ÿ =๐ŸŽ ๐’Ž๐’†๐‘ฝ โ„ซ ๐Ÿ‘ Solve for LL energies and extract ๐œš ๐‘ฅ๐‘ฅ ๐ต ๐‘ง ๐›ผ 10 =53๐‘š ๐‘’๐‘‰โ„ซ ๐›ฝ 10 =28.5 ๐‘š๐‘’๐‘‰โ„ซ ๐œธ ๐Ÿ๐ŸŽ =๐ŸŽ ๐’Ž๐’†๐‘ฝ โ„ซ ๐Ÿ‘ In 2D systems: ๐›ฝ= ๐‘˜ ๐‘ง 2 ๐›พ ; ๐‘˜ ๐‘ง 2 โ‰ˆ ๐œ‹ ๐‘‘ 2 Compare data to QM LL simulations with the MB mechanism [4] ๏ƒจ Valid for infinite square wellโ€ฆ ๐‘š โˆ— =0.04 ๐‘š 0 ; ๐‘” โˆ— =โˆ’11.5 Cubic Dresselhaus term set to zero for good fits!?!? [4] R. Winkler, Spin-orbit Coupling Effects in Two-dimensional Electron and Hole Systems, Springer 2003

9 Two Carrier Regime ๐‘’ โˆ’ in InAs present with holes in GaSb simultaneously Investigate influence of hybridization on โˆ† ๐‘› ๐‘๐น through magnetoresistance traces on line ฮ™ฮ™ Hole concentration increases from point 1 to 13 ๏ƒ  13: ๐‘› โ„Ž โ‰ˆ ๐‘› ๐‘’ โˆ’ ๐ธ ๐น near hybrid. gap

10 Magnetoresistance Data
Traces with and without beating โˆ† ๐‘› ๐‘๐น,1โˆ’3 =1.7โˆ™ m โˆ’2 โˆ† ๐‘› ๐‘๐น,4โˆ’5 ๏ƒ  no beating ๏ƒ  no ZFDD extractable Non-monotonic behavior! Band structure calculations agree qualitatively for first 10 points

11 Lack of Beating Two possible reasons:
Strong asymmetry between spin species determines visibility ( ๐ด ๐‘ข๐‘ โ‰ซ ๐ด ๐‘‘๐‘œ๐‘ค๐‘› ) ๐ด ๐‘†๐‘‘๐ป โˆ ๐‘’๐ต ๐‘š โˆ— 3 expโก โˆ’๐œ‹ ๐œ” ๐‘ ๐œ [5] When approaching hybrid. gap ๐‘š โˆ— and ๐œ are very dissimilar ๏ƒ  visibility reduced below experimental detection limits Energy window with single spin band present [6] No beating possible They can not determine which is the cause [5] J. Luo et al., PRB, 41, (1990) [6] F. Nichele et al., ArXiv (2016),

12 Conclusion Study of SOI in InAs/GaSb DQW by top and back gating
Tunable in electron-only regime ๏ƒจ extract Rashba and Dresselhaus Non-monotonic spin splitting behavior in two carriers regime ๏ƒจ crossing of spin bands due to hybridization

13 Thanks for listening!!

14 ๐ต โŠฅ =2T

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18 Christopher Schierholz โ€“ Rashba Spin-Orbit Interaction in Low and High Magnetic Fields


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