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Hitachi Cambridge Laboratory, UK National Physical Laboratory, UK Texas A&M University, USA

Spin Hall effect. J. Wunderlich (1) , B. Kaestner (1,2) , J. Sinova (3) , T. Jungwirth (4,5). Hitachi Cambridge Laboratory, UK National Physical Laboratory, UK Texas A&M University, USA Institute of Physics ASCR, Czech Republic University of Nottingham, UK.

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Hitachi Cambridge Laboratory, UK National Physical Laboratory, UK Texas A&M University, USA

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  1. Spin Hall effect J. Wunderlich(1), B. Kaestner(1,2), J. Sinova (3), T. Jungwirth (4,5) • Hitachi Cambridge Laboratory, UK • National Physical Laboratory, UK • Texas A&M University, USA • Institute of Physics ASCR, Czech Republic • University of Nottingham, UK Collaborators: Allan MacDonald, Dimitri Culcer,Ewelina Hankeiwc,Qian Niu, Kentaro Nomura,Nikolai Sinitsyn, Laurens Molenkamp, Winfried Teizer

  2. OUTLINE: - Theory remarks - Comments on experiments Kerr microscope Co-planar spin LED SHE in a bulk semiconductor SHE in a 2D hole gas [Wunderlich et. al., Phys. Rev. Lett. 94, 047204] [Kato et. al., Science 306, 1910]

  3. SHE - Theory(http://unix12.fzu.cz/msnew) • Schmeltzer:2005_a • D. Schmeltzer, "The Non-Dissipative Spin-Hall Conductivity and the Identification of the Conserved Current", (2005), preprint cond-mat/0504035: on-line • Wu:2005_a • M. W. Wu and J. Zhou, "Spin-Hall effect in two-dimensional mesoscopic hole systems", (2005), preprint cond-mat/0503616: on-line • Erlingsson:2005_a • Sigurdur I. Erlingsson and Daniel Loss, "Determining the spin Hall conductance via charge transport", (2005), preprint cond-mat/0503605: on-line • Zhang:2005_b • Ping Zhang and Junren Shi and Di Xiao and Qian Niu, "Conserved Effective Spin Current in Spin-Orbit Coupled Systems", (2005), preprint cond-mat/0503505: on-line • Sugimoto:2005_a • Naoyuki Sugimoto, Shigeki Onoda, Shuichi Murakami, Naoto Nagaosa, "Intrinsic vs. extrinsic spin Hall effect in the disordered Rashba Mode", (2005), preprint cond-mat/0503475: on-line • Bleibaum:2005_a • O. Bleibaum, "Spin-Hall effect in a dirty Rashba semiconductor", (2005), preprint cond-mat/0503471: on-line • Nikolic:2005_a • Branislav K. Nikolic, Liviu P. Zarbo, and Sven Welack, "Where is transverse "force" in the intrinsic spin Hall effect?", (2005), preprint cond-mat/0503415: on-line • Liu:2005_b • S. Y. Liu and X. L. Lei, "Disorder effects on dissipationless spin-Hall current in a diffusive Rashba two-dimensional heavy-hole system", (2005), preprint cond-mat/0503352: on-line • Hu:2005_b • Jiangping H, "Topological orbital angular momentum Hall current", (2005), preprint cond-mat/0503149: on-line • Chen:2005_a • W.Q. Chen, Z.Y. Weng, and D.N. Sheng, "Numerical Study of the Spin Hall Conductance in the Luttinger Model", (2005), preprint cond-mat/0502570: on-line • Entin-Wohlman:2005_a • O. Entin-Wohlman, A. Aharony, Y. M. Galperin, V. I. Kozub, and V. Vinokur, "Orbital ac spin-Hall effect in the hopping regime", (2005), preprint cond-mat/0502478: on-line • Liu:2005_a • S. Y. Liu and X. L. Lei, "Vanishing of the Dissipationless Spin Hall Effect in a Diffusive Two-Dimensional Electron Gas with Spin-Orbit Coupling", (2005), preprint cond-mat/0502392: on-line • Yao:2005_a • Y. Yao, and Z. Fang, "Intrinsic Spin Hall Effect in Semiconductors and Simple Metals: First-Principles Calculations", (2005), preprint cond-mat/0502351: on-line • Bernevig:2005_a • B. Andrei Bernevig, Taylor L. Hughes, Shou-Cheng Zhang, "Orbitronics: the Intrinsic Orbital Hall Effect in p-Doped Silicon", (2005), preprint cond-mat/0502345: on-line • Li:2005_a • Jian Li, Liangbin Hu, and Shun-Qing Shen, "Spin resolved Hall effect driven by spin-orbit couplin", (2005), preprint cond-mat/0502102: on-line • Hu:2005_a • Jiangping Hu, "Spin Polarization and Dichroism Effects by Electric Field", (2005), preprint cond-mat/0502005: on-line • Lou:2005_a • Ping Lou and Tao Xiang, "Spin Hall current and two-dimensional magnetic monopole in a Corbino disk", (2005), preprint cond-mat/0501307: on-line • Nikolic:2004_b • Nikolic et al., "Non-Equilibrium Spin Accumulation due to the Spin Hall Effect in Mesoscopic Two-Probe Ballistic Spin-Orbit ", (2004), preprint cond-mat/0412595: on-line • Bernevig:2004_e • B. Andrei Bernevig and Shou-Cheng Zhang, "Intrinsic Spin-Hall Effect in n-Doped Bulk GaAs", (2004), preprint cond-mat/0412550: on-line • Kou:2004_a • Su-Peng Kou, Xiao-Liang Qi, and Zheng-Yu Weng, "Conserved Dissipationless Spin Currents in a Doped Mott Insulator", (2004), preprint cond-mat/0412146: on-line • Mele:2004_a • C.L. Kane and E.J. Mele, "Quantum Spin Hall Effect in Graphene", (2004), preprint cond-mat/0411737: on-line • Bernevig:2004_d • B. Andrei Bernevig, Xiaowei Yu, Shou-Cheng Zhang, "Maxwell Equation for the Coupled Spin-Charge Wave Propagation", (2004), preprint cond-mat/0411276: on-line

  4. Sun:2004_a • Qing-feng Sun, Jian Wang, Hong Guo, "Quantum transport theory for nanostructures with Rashba spin-orbital interaction", (2004), preprint cond-mat/0411469: on-line • Shekhter:2004_a • A. Shekhter, et al., "Chiral spin resonance and spin-Hall conductivity in the presence of the electron-electron interactions", (2004), preprint cond-mat/0411239: on-line • Serebrennikov:2004_a • Yuri A. Serebrennikov, "Gometric spin dephasing of carriers with strong spin-orbit coupling", (2004), preprint cond-mat/0411683: on-line • Chang:2004_a • Ming-Che Chang, "The effect of in-plane magnetic field on the spin Hall effect in Rashba-Dresselhaus system", (2004), preprint cond-mat/cond-mat/0411697: on-line • Liu:2004_d • S. Y. Liu, X. L. Lei, "Spin Hall Effect in a Diffusive Rashba Two-dimensional Electron Gas", (2004), preprint cond-mat/0411629: on-line • Bernevig:2004_c • B. Andrei Bernevig and Shou-Cheng Zhang, "Intrinsic Spin Hall Effect in the Two Dimensional Hole Gas", (2004), preprint cond-mat/0411457: on-line • Mal'shukov:2004_a • A.G. Mal'shukov and K.A. Chao, "Spin-Hall conductivity of a disordered 2D electron gas with Dresselhaus spin-orbit interaction", (2004), preprint cond-mat/0410607: on-line • Souma:2004_a • Satofumi Souma and Branislav K. Nikolic, "Spin Hall Current Driven by Quantum Interferences in Mesoscopic Rashba Rings", (2004), preprint cond-mat/0410716: on-line • Shen:2004_b • Shun-Qing Shen, et al., "Resonant spin Hall conductance in quantum Hall systems lacking bulk and structural inversion symmetry", (2004), preprint cond-mat/0410169: on-line • Sheng:2004_a • L. Sheng, D. N. Sheng, and C. S. Ting, "Spin-Hall Effect in Two-Dimensional Electron Systems with Rashba Spin-Orbit Coupling and Disorder", (2004), preprint cond-mat/0409038: on-line • Nikolic:2004_a • Branislav K. Nikolic, Liviu P. Zarbo, and Satofumi Souma, "Mesoscopic Spin Hall Effect in Multiprobe Semiconductor Bridges", (2004), preprint cond-mat/0408693: on-line • Bernevig:2004_b • B. Andrei Bernevig and Shou-Cheng Zhang, "Spin Splitting and Spin Current in Strained Bulk Semiconductors", (2004), preprint cond-mat/0408442: on-line • Khaetskii:2004_a • Alexander Khaetskii, "Nonexistence of intrinsic spin currents", (2004), preprint cond-mat/0408136: on-line • Rashba:2004_c • Emmanuel I. Rashba, "Spin Dynamics and Spin Transport", (2004), preprint cond-mat/0408119: on-line • Wang:2004_b • Xindong Wang and X.-G. Zhang, "Spin symmetry and spin current of helicity eigenstates of the Luttinger Hamiltonian", (2004), preprint cond-mat/0407699: on-line • Dimitrova:2004_b • Ol'ga V. Dimitrova, "Spin-Hall Conductivity and Pauli Susceptibility in the Presence of Electron-Electron Interactions", (2004), preprint cond-mat/0407612: on-line • Chalaev:2004_a • Oleg Chalaev, Daniel Loss, "Spin-Hall conductivity due to Rashba spin-orbit interaction in disordered systems", (2004), preprint cond-mat/0407342: on-line • Schmeltzer:2004_a • D. Schmeltzer, "Topological spin current", (2004), preprint cond-mat/0406565: on-line • Zhang:2004_a • Ping Zhang and Qian Niu, "Charge-Hall effect driven by spin force: reciprocal of the spin-Hall effect", (2004), preprint cond-mat/0406436: on-line • Dimitrova:2004_a • Ol'ga V. Dimitrova, "Universal value of Spin-Hall Conductivity of 2D Rashba metal with impurities", (2004), preprint cond-mat/0405339: on-line • Murakami:2004_a • Shuichi Murakami, "Spin Hall Effect in p-type Semiconductors", (2004), preprint cond-mat/0405003: on-line • Xiong:2004_a • Ye Xiong and X.C. Xie, "Spin Hall Conductance in Disordered Two-Dimensional Electron Systems", (2004), preprint cond-mat/0403083: on-line • Dyakonov:2004_a • M. I. Dyakonov, "Spintronics?", (2004), preprint cond-mat/0401369: on-line • -------- 2005 -------- • Raimondi:2004_a • Roberto Raimondi and Peter Schwab, "Spin-Hall effect in a disordered 2D electron-system", Phys. Rev. B 71, 033311 (2005): on-line, preprint cond-mat/0408233: on-line • Zhang:2004_b • S. Zhang and Z. Yang, "Intrinsic Spin and Orbital-Angular-Momentum Hall Effect", Phys. Rev. Lett. 94, 066602 (2005): on-line, preprint cond-mat/0407704: on-line

  5. Nomura:2004_a • K. Nomura, et al., "Non-vanishing spin Hall currents in disordered spin-orbit coupling systems", Phys. Rev. B 71, 041304 (2005): on-line, preprint cond-mat/0407279: on-line • Schliemann:2004_a • John Schliemann, Daniel Loss, "Spin-Hall transport of heavy holes in III-V semiconductor quantum wells", Phys. Rev. B 71, 085308 (2005): on-line, preprint cond-mat/0405436: on-line • -------- 2004 -------- • Rashba:2004_d • Emmanuel I. Rashba, "Sum rules for spin-Hall conductivity cancelation", Physica B 70, 201309(R) (2004): on-line, preprint cond-mat/0409476: on-line • Hankiewicz:2004_b • E. M. Hankiewicz, et al., "Manifestation of the spin-Hall effect through transport measurements in the mesoscopic regime", Phys. Rev. B 70, 241301(R) (2004): on-line, • Ma:2004_a • Xiaohua Ma, et al., "Influences of spin accumulation on the intrinsic spin Hall effect in two dimensional electron gases with Rashba spin-orbit coupling", Phys. Rev. B 70, 195343 (2004): on-line, • Mishchenko:2004_a • E.G. Mishchenko, et al., "Spin current and polarization in impure 2D electron systems with spin-orbit coupling", Phys. Rev. Lett. 93, 226602 (2004): on-line, preprint cond-mat/0406730: on-line • Bernevig:2004_a • B. A. Bernevig, "On the nature of spin currents", Phys. Rev. B 71, 073201 (2004): on-line, preprint cond-mat/0406153: on-line • Murakami:2004_b • Shuichi Murakami, Naoto Nagaosa, Shou-Cheng Zhang, "Spin Hall Insulator", Phys. Rev. Lett. 93, 156804 (2004): on-line, preprint cond-mat/0406001: on-line • Lee:2004_a • Wei-Li Lee, et al., "Dissipationless Anomalous Hall Current in the Ferromagnetic Spinel CuCr2Se4-xBrx", Science 303, 1647 (2004): on-line, preprint cond-mat/0405584: on-line • Zutic:2004_a • Igor Zutic, Jaroslav Fabian and S. Das Sarma, "Spintronics: Fundamentals and applications", Rev. Mod. Phys. 76, 323 (2004): on-line, preprint cond-mat/0405528: on-line • Murakam:2004_a • Shuichi Murakami, "Absence of vertex correction for the spin Hall effect in p-type semiconductors", Phys. Rev. B 69, 241202 (2004): on-line, preprint cond-mat/0405001: on-line • Rashba:2004_b • Emmanuel I. Rashba, "Spin currents, spin populations, and dielectric function", Phys. Rev. B 70, 161201 (2004): on-line, preprint cond-mat/0404723: on-line • Shen:2004_a • Shun-Qing Shen, et al., "Resonant Spin Hall Conductance in Two-Dimensional Electron Systems with Rashba Interaction in a Magnetic Field", Phys. Rev. Lett 92, 256603 (2004): on-line, • Inoue:2004_a • Jun-ichiro Inoue, et al., "Suppression of the Persistent Spin Hall Current by Defect Scattering", Phys. Rev. B 70, 041303 (2004): on-line, preprint cond-mat/0402442: on-line • Hu:2004_a • Liangbin Hu, et al., "Effects of spin imbalance on the electric-field-driven quantum dissipationless spin current in p-doped semiconductors", Phys. Rev. B 70, 235323 (2004): on-line, • Bernevig:2003_a • Bogdan et al., "Dissipationless spin current in anisotropic p-doped semiconductors", Phys. Rev. B 70, 113301 (2004): on-line, preprint cond-mat/0311024: on-line • Shen:2003_a • Shun-Qing Shen, "Spin Hall effect and Berry phase in two dimensional electron gas", Phys. Rev. B 70, 081311 (2004): on-line, preprint cond-mat/0310368: on-line • Sinitsyn:2003_a • N. A. Sinitsyn, et al., "Spin-Hall and spin-diagonal conductivity in the presence of Rashba and Dresselhaus spin-orbit coupling", Phys. Rev. B 70, 081312(R) (2004): on-line, • Schliemann:2004_b • John Schliemann and Daniel Loss, "Dissipation effects in spin-Hall transport of electrons and holes", Phys. Rev. B 69, 165315 (2004): on-line, preprint cond-mat/0310108: on-line • Culcer:2004_a • Dimitrie Culcer, et al., "Semiclassical theory of spin transport in spin-orbit coupled systems", Phys. Rev. Lett. 93, 046602 (2004): on-line, preprint cond-mat/0309475: on-line • -------- 2003 -------- • Rashba:2003_a • Emmanuel I. Rashba, "Spin currents in thermodynamic equilibrium: The challenge of discerning transport currents", Phys. Rev. B 68, 241315 (2003): on-line • Culcer:2003_a • Dimitrie Culcer, Allan MacDonald, Qian Niu, "Anomalous Hall effect in paramagnetic two dimensional systems", Phys. Rev. B 68, 045327 (2003): on-line, preprint cond-mat/0311147: on-line • Hu:2003_a • Jiangping Hu, Bogdan A. Bernevig and Congjun Wu, "Spin current in spin-orbit coupling systems", Int. J. Mod. Phys. B 17, 5991 (2003), preprint cond-mat/0310093: on-line • Murakami:2003_b • Shuichi Murakami, et al., "SU(2) Non-Abelian holonomy and dissipationless spin current in semiconductors", Phys. Rev. B B 69, 235206 (2003): on-line, preprint cond-mat/0310005: on-line • Sinova:2004_a • Jairo Sinova, et al., "Universal Intrinsic Spin-Hall Effect", Phys. Rev. Lett. 92, 126603 (2004): on-line, preprint cond-mat/0307663: on-line • Murakami:2003_a • Shuichi Murakami, Naoto Nagaosa, Shou-Cheng Zhang, "Dissipationless Quantum Spin Current at Room Temperature", Science 301, 1348 (2003): on-line, preprint cond-mat/0308167: on-line • --------

  6. SHE - Experiment(http://unix12.fzu.cz/msnew) • Kato:2005_a • Y. K. Kato, et al., "Electrical initialization and manipulation of electron spins in an L-shaped strained n-InGaAs channel", (2005), preprint cond-mat/0502627: on-line • Wunderlich:2004_a  • J. Wunderlich, et al. "Experimental observation of the spin-Hall effect in a two dimensional spin-orbit coupled semiconductor system", Phys. Rev. Lett. 94, 047204 (2005): • preprint cond-mat/0410295: on-line • Kato:2004_d  • Y. K. Kato, R. C. Myers, A. C. Gossard, and D. D. Awschalom, "Observation of the Spin Hall Effect in Semiconductors", Science 306, 1910 (2004): on-line

  7. B _ _ _ _ _ _ _ _ _ _ _ FL + + + + + + + + + + + + + I V Ordinary and quantum Hall effects Lorentz force deflect like-charge particles Quantum Resistance standard; fractional-charge carriers Ordinary: Sign and density of carriers; holes in SC

  8. majority _ _ _ FSO _ FSO I minority V Anomalous Hall effect Spin-orbit coupling “force” deflects like-spin particles InMnAs Simple electrical measurement of magnetization

  9. _ _ _ FSO _ non-magnetic FSO I V=0 Spin Hall effect Spin-orbit coupling “force” deflects like-spinparticles Spin-current generation in non-magnetic systems without applying external magnetic fields Spin accumulation without charge accumulation excludes simple electrical detection

  10. k E Beff Spin-orbit coupling (relativistic effect) Produces an electric field Ingredients: - potential V(r) - motion of an electron E In the rest frame of an electron the electric field generates and effective magnetic field - gives an effective interaction with the electron’s magnetic moment

  11. skew scattering Skew scattering off impurity potential (Extrinsic SHE/AHE) If only this SO effect then much too weak to give a sizable SHE/AHE

  12. SO-coupling from host atoms (Intrinsic SHE/AHE) l=0 for electrons  weak SO l=1 for holes  strong SO Enhanced in asymmetric QW

  13. Intrinsic AHE approach explains many experiments • (Ga,Mn)As systems [Jungwirth et al. PRL 02, APL 03] • Fe [Yao, Kleinman, Macdonald, Sinova, • Jungwirth et al PRL 04] • Layered 2D ferromagnets such as SrRuO3 and pyrochlore ferromagnets [Onoda and Nagaosa, J. Phys. Soc. Jap. 01,Taguchi et al., Science 01, Fang et al Science 03, Shindou and Nagaosa, PRL 01] • Manganites, [Ye et al. PRL 99] • Ferromagnetic spinel CuCrSeBr [Lee et al. Science 04] Experiment sAH  1000 (W cm)-1 Theroy sAH  750 (W cm)-1

  14. INTRINSIC SPIN-HALL EFFECT:[Murakami, Nagaosa, Zhang, Science 2003 (cond-mat/0308167)Sinova, Culcer, Niu, Sinitsyn, Jungwirth, MacDonald, PRL 2004 (cont-mat/0307663)] Let’s start with a simple model: Rashba SO coupling in a 2DEGs Inversion symmetry  no R-SO Broken inversion symmetry  R-SO [Bychkov and Rashba 84]

  15. Heuristic argument: z-component of spin due to precession in effective "Zeeman" field Classical dynamics in k-dependent (Rashba) field: LLG equations for small drift adiabatic solution: 

  16. Spin Hall conductivity

  17. Classical and Kubo formula give the same spin-Hall conductivity Color plot of spin-Hall conductivity: yellow=e/8π and red=0

  18. Disorder effects: finite lifetime (Born approximation) for Rashba 2DEG  intrinsic SHE

  19. Disorder effects: beyond the Born approximation for Rashba 2DEG Question: Are there any other major effects beyond the finite life time broadening? Can vertex corrections be ignored? Mal'shukov et al, PRL 04 Raimondi et al, PRB 04 Khaetskii, cond-mat/0408136 Loss et al, cond-mat/0407342 v2 Inoue, Bauer, Molenkamp PRB 04 Ladder sum vertex correction:

  20. Spin Hall effect ? Intrinsic cancelled by vertex corrections for infinitely weak disorder Extrinsic too weak to give any sizable effect

  21. Ways to solve (go around) the controversy: - Skew scattering in SO-coupled bands [in the spirit of Dyakonov and Perel PLA '71 and Hirsch PRL '99]  no detailed theory done yet - Intrinsic SHE in Rashba-SO systems beyond perturbation theory by solving Kubo formula exactly  inconclusive (finite-size effects) [Nomura et al. PRB '05] - Other than Rashba-SO systems (intrinsic AHE explains experiments here) [Bernevig, Zhang, cond-mat/0411457, cond-mat/0412550  vertex corrections vanish in all other studied SO-systems (bulk, 2DHG,..)

  22. - Look at transport in mesoscopic systems instead of conductivity in the thermodynamic limit [Nikolic et al., cond-mat/0412595] [Hankiewicz et al., PRB 04] SHE in 2DHG more robust than in Rashba 2DEG

  23. - Measure the effect Kato, Myars, Gossard, Awschalom, [Science 306, 1910] "Observation of the spin Hall effect in semiconductors" Local Kerr effect in n-type GaAs and InGaAs: ~0.03% polarization Bulk semiconductor  stronger disorder n-type material  weaker SO-coupling Not in the intrinsic SHE regime

  24. Experiment “A” LED 1 a +Ip CP [%] -Ip Experiment “B” +Ip LED 1 CP [%] LED 2 E [eV] Wunderlich, Kästner, Sinova, Jungwirth, [Phys. Rev. Lett. 94, 047204] Experimental observation of the spin-Hall effect in a two dimensional spin-orbit coupled semiconductor system Co-planar spin LED in GaAs 2D hole gas: ~1% polarization

  25. 3D electron-2D hole Recombination 9 2.5 a η [meV] 1.5 S [e/8] 5 + - E [meV] HH+ 0.5 1 HH- 10 20 30 LH p2D [1011 cm-2] -0.2 0.0 0,2 ky [nm-1] Self-consistent LDA & 6-band calculations for the [001] QW Modulation doping  weak disorder p-type asymmetric QW  strong SO Close to the intrinsic SHE regime

  26. A dissipationless remark ...

  27. Dissipative spin-polarized currents in non-magnetic systems at B=0 Spin-current is along the applied electric field  proportional to non-equilibriumdistribution function asymmetric scattering involving spin-flip [Ganichev et al.,cond-mat/0403641, Silov et al. APL 04]

  28. Dissipationless intrinsic spin Hall effect ● Heuristic argument: transverse spin current generated between scattering events Sinova, Culcer, Niu, Sinitsyn, Jungwirth, MacDonald, PRL 92, 126603 (2004) ● Boltzman equation for current: transverse anomalous velocity in the equilibrium band structure due to combined E and SO effects Jungwirth, Niu, MacDonald, Phys. Rev. Lett. (2002) Murakami, Nagaosa, Zhang, Science 301, 1348-1351 (2003). normal group velocity anomalous velocity Berry curvature: M.V. Berry, Proc. Royal Soc. London (1984)

  29. Caution: the dissipationless transverse intrinsic SHE is accompanied by a dissipative longitudinal response to the electric field

  30. Conventional vertical spin-LED Novel co-planar spin-LED Y. Ohno et al.: Nature 402, 790 (1999) R. Fiederling et al.: Nature 402, 787 (1999) B. T. Jonker et al.: PRB 62, 8180 (2000) X. Jiang et al.: PRL 90, 256603 (2003) R. Wang et al.: APL 86, 052901 (2005) … ● Light emission near edge of the 2DHG ● 2DHG with strong and tunable SO ●Spin detection directly in the 2DHG ● No hetero-interface along the LED current 2DHG 2DEG Spin polarization detected through circular polarization of emitted light

  31. Conventional vertical spin-LED Novel co-planar spin-LED Y. Ohno et al.: Nature 402, 790 (1999) R. Fiederling et al.: Nature 402, 787 (1999) B. T. Jonker et al.: PRB 62, 8180 (2000) X. Jiang et al.: PRL 90, 256603 (2003) R. Wang et al.: APL 86, 052901 (2005) … ● No hetero-interface along the LED current ● Spin detection directly in the 2DHG ●Light emission near edge of the 2DHG ● 2DHG with strong and tunable SO 2DHG 2DEG Spin polarization detected through circular polarization of emitted light

  32. CO-PLANAR pn - JUNCTION Wafer design based on Schrödinger-Poisson simulations

  33. n - region p - region Light emission ● 2D transport characteristics Carrier density: n = 0.8  1012 cm-2p = 2.0  1012 cm-2 Mobility: µHn  2900 cm2/Vs µHp  3400 cm2/Vs pn - junction ● Light emission near junction in p-region ● Light emission for eVBias  EG ● Rectifying Reverse breakdown: VR = -11.5V (T = 4.2K)

  34. - + 1m Band-flattening if forward biased Electron – 2D holes recombination possible E p - AlGaAs GaAs z [nm] z Energy [eV]

  35. Sub GaAs gap spectra analysis: PL vs EL X : bulk GaAs excitons I : recombination with impurity states

  36. Sub GaAs gap spectra analysis: PL vs EL + - X : bulk GaAs excitons I : recombination with impurity states B (A,C): 3D electron – 2D hole recombination

  37. Sub GaAs gap spectra analysis: PL vs EL ++ -- X : bulk GaAs excitons I : recombination with impurity states B (A,C): 3D electron – 2D hole recombination Bias dependent emission wavelength for 3D electron – 2D hole recombination [A. Y. Silov et al., APL 85, 5929 (2004)]

  38. 2DHG 2DEG CONTROL EXPERIMENT p-n junction current only (no SHE driving current)

  39. Circular Polarization of EL detected at perpendicular to 2DHG plane

  40. Inplane Circular Polarization (= 85º) detected at B =+ 3T.

  41. Inplane Circular Polarization (= 85º) detected at B = 3T.

  42. Circular Polarization In-plane detection angle

  43. Circular Polarization In-plane detection angle Perp.-to plane detection angle  NO perp.-to-plane component of polarization at B=0  B≠0 behavior consistent with SO-split HH subband

  44. SHE           j           Spin Hall Effect • Perpendicular-to-plane spin-polarization

  45. 2DEG VT 2DHG VD EXPERIMENT Spin Hall Effect

  46. Experiment “A” Experiment “B” Spin Hall Effect Device

  47. Experiment “A” Experiment “B” Opposite perpendicular polarization for opposite Ip currents or opposite edges  SPIN HALL EFFECT

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