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Detection of current induced Spin polarization with a co-planar spin LED

Detection of current induced Spin polarization with a co-planar spin LED. J. Wunderlich (1) , B. Kästner (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

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Detection of current induced Spin polarization with a co-planar spin LED

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  1. Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (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 Thanks to A.H. MacDonald, University of Texas

  2. OUTLINE • Current induced spin-polarization: • Levitov, Mal’shukov, Spin-Hall • Experimental results • Conclusion / Outlook

  3. -0.2 0.0 0,2 ky [nm-1] “Levitov effect” “Mal’shukov effect” - by asymmetrical optical recombination in a pn-junction • by applying an electric field Ex [Mal’shukov et al., PRB 65 241308(R) (2002)] [Levitov et al , Zh. Eksp. Teor. Fiz. 88, 229 (1985)] • Inplane polarization for a [001] grown GaAs quantum well

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

  5. 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

  6. 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

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

  8. 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)

  9. - + 1m Band-flattening if forward biased Electron – 2D holes recombination possible E p - AlGaAs GaAs z [nm] z Energy [eV]

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

  11. 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

  12. 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)]

  13. 2DHG 2DEG EXPERIMENT Occupation-asymmetry mostly due to “Mal’shukov effect”

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

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

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

  17. Circular Polarization In-plane detection angle

  18. 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

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

  20. 2DEG VT 2DHG VD EXPERIMENT Spin Hall Effect

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

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

  23. Comparing extrinsic and intrinsic SHE contribution for our system by taking HH mass and mobility in account: • within the intrinsic SHE regime • larger contribution from intrinsic SHE

  24. Outlook SHE in 2DHG and 2DEG n GATE GATE GATE GATE j j p 2DHG 2DEG 2DHG SHE in with differently confined 2DHG 2DEG 2DHG 2DEG Changing confinement, charge carrier density, via gating, wafer design, temperature dependence,etc.

  25. Locally induced Electron spin polarization magnetic particle on top of 2DEG channel MFM micrograph

  26. Conclusion • Spin polarization due to occupation-asymmetry • Detection of in-plane net-spin-polarization • spin-Hall effect in hole system • Detection of perpendicular-to-plane polarization

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