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From ferromagnetic to non-magnetic semiconductor spintronics: Spin-injection Hall effect

From ferromagnetic to non-magnetic semiconductor spintronics: Spin-injection Hall effect. Tom as Jungwirth. Universit y of Nottingham Bryan Gallagher, Richard Campion, Kevin Edmonds , Andrew Rushforth, et al. Institute of Physics ASCR

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From ferromagnetic to non-magnetic semiconductor spintronics: Spin-injection Hall effect

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  1. From ferromagnetic to non-magnetic semiconductor spintronics: Spin-injection Hall effect Tomas Jungwirth University of Nottingham Bryan Gallagher, Richard Campion, Kevin Edmonds, Andrew Rushforth, et al. Institute of Physics ASCR Jairo Sinova, Karel Výborný, Jan Zemen, Jan Mašek, Alexander Shick, František Máca, Jorg Wunderlich, Vít Novák,Kamil Olejník, et al. Hitachi Cambridge, Univ. Cambridge Jorg Wunderlich, Andrew Irvine, Byonguk Park, etal. Texas A&M University Jairo Sinova, Liviu Zarbo, et al.

  2. AMR and GMR (TMR) sensors: dawn of spintronics Inductive read elements Magnetoresistive read elements 1980’s-1990’s

  3. Ferromagnetism only  giant (tunnel) magnetoresistance Ferromagnetism & spin-orbit coupling  anisotropic magnetoresistance ~ 100% MR effect ~ 1% MR effect magnetization current Lord Kelvin 1857 Fert, Grunberg et al. 1988

  4. Renewed interest in SO induced MRs in ferromagnetic semiconductors Ohno Science ’98 ~ 1000% MR effect & gate controlled Wunderlich et al. PRL ’06 Schlapps et al. PRB `09 Coulomb blockade AMR: likely the most sensitive spintronic transistors to date p- or n-type FET depending on magnetization  non-volatile programmable logic, etc.

  5. B V SO induced MRs: AMR & anomalous Hall effect Ordinary Hall effect: response in normal metals to external magnetic field via Lorentz force Anomalous Hal effect: response to internal spin polarization in ferromagnets via spin-orbit coupling Hall 1879 Hall 1881 _ _ FSO M _ _ FL I I V Tc in (Ga,Mn)As upto ~190 K but AHE survives and dominates HE far above Tc AHE OHE Ruzmetov et al. PRB ’04

  6. j=3/2 HH HH & LH Fermi surfaces (Ga,Mn)As: simple band structure of the host SC Quantitative AHE theory Jungwirth et al. PRL ’02 Spherical HH Kohn-Luttinger 3D model  Rashba and Dresselhaus 2D models

  7. Intense theory research of AHE in model 2D R&D systems Nagaosa et al RMP ‘’09 in press (arXiv:0904.4154)

  8. B _ _ _ FSO _ FSO I || E V Taming spins in non-magnetic materials: spin-Hall effect Ordinary Hall effect: response in normal metals to external magnetic field via classical Lorentz force Anomalous Hal effect: response to internal spin polarization in ferromagnets via quantum-relativistic spin-orbit coupling Hall 1879 Hall 1881 _ _ FSO M _ _ FL I I V Spin Hall effect spin-dependent deflection  transverse edge spin polarization Wunderlich et al. arXives ’04 (PRL ’05) Kato et al. Science ’04

  9. Polarized EL from a planar LED Theory and experiment: ~10% polarization over ~10nm wide edge region

  10. More taming of spins by spin-orbit coupling Spin-injection from a ferromagnet Ferromagnet Wunderlich et al. Nature Phys.‘09

  11. More taming of spins by spin-orbit coupling Spin-injection by incident circularly polarized light + Wunderlich et al. Nature Phys.‘09

  12. More taming of spins by spin-orbit coupling Spin-injection Hall effect + + + + – – – Spin-dependent deflection due to spin-orbit coupling Wunderlich et al. Nature Phys.‘09

  13. More taming of spins by spin-orbit coupling Spin-injection Hall effect + + + + + + + + + + + + + – – – – – – – – – – – – Spin-dependent deflection due to spin-orbit coupling  transverse (Hall) electrical voltage in steady state Wunderlich et al. Nature Phys.‘09

  14. More taming of spins by spin-orbit coupling Spin-injection Hall effect + + + – – + + – – + + – – Built-in electric fields in SC structure  another spin-orbit coupling effect which can lead to spin precession Hall voltages measure local spin orientation Bernevig et al., PRL`06, Wunderlich et al. Nature Phys.‘09

  15. More taming of spins by spin-orbit coupling Spin-injection Hall effect + + + – – + + – – + + – – Built-in electric fields in SC structure can be modified by external gate voltage Hall signals changed by gate  transverse-voltage spintronic transistor Bernevig et al., PRL`06, Wunderlich et al. Nature Phys.‘09

  16. VG More taming of spins by spin-orbit coupling Spin-injection Hall effect + + + – – + + – – + + – – + + – – + + – – Built-in electric fields in SC structure can be modified by external gate voltage Hall signals changed by gate  transverse-voltage spintronic transistor Bernevig et al., PRL`06, Wunderlich et al. Nature Phys.‘09

  17. VH h h h h h h e e e e e e Optical injection of spin-polarized charge currents into Hall bars  GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell 2DHG 2DEG

  18. Optical spin-generation area near the p-n junction Simulated band-profile p-n junction bulit-in potential (depletion length ) ~ 100 nm  self-focusing of the generation area of counter-propagating e- and h+ Hall probes further than 1m from the p-n junction  safely outside the spin-generation area and/or masked Hall probes

  19. Experimental observation of the SIHE

  20. SIHE linear in degree of polarization and spatially varying

  21. Spin dynamics in Rashba&Dresselhaus SO-couped 2DEG  > 0,  = 0  = 0,  < 0 k-dependent SO field  strong precession & spin-decoherence due to scattering

  22. No decoherence for || = || & channel  SO field Bernevig et al PRL’06 [110] [1-10]

  23. Diffusive spin dynamics & Hall effect due to skew scattering precession-length (~1m) >> mean-free-path (~10 nm) ~10nm

  24. Conclusions SIHE: high-T SO only spintronics in non-magnetic systems • Basic studies of spin-charge dynamics and Hall effect in non-magnetic systems with SO coupling • Spin-photovoltaic cell: polarimeter on a SC chip requiring no magnetic elements, external magnetic field, or bias; unconventional laser displacement sensor with the resolution defined by the spin-precession length built in the SC • SIHE can be tuned electrically by external gate and combined with electrical spin- injection from a ferromagnet (e.g. Fe/Ga(Mn)As structures)

  25. SIHE vs other spin-detection tools in semiconductors • Magneto-optical imaging non-destructive  lacks nano-scale resolution and only an optical lab tool Crooker et al. JAP’07, others • MR Ferromagnet  electrical  requires semiconductor/magnet hybrid design & B-field to orient the FM Ohno et al. Nature’99, others • spin-LED  all-semiconductor  requires further conversion of emitted light to electrical signal

  26. Spin-injection Hall effect  non-destructive  electrical  100-10nm resolution with current lithography in situ directly along the SC channel & all-SC requiring no magnetic elements in the structure or B-field

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