Institute of Physics ASCR Hitachi Cambridge, Univ. Cambridge 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 Karel Výborný, Jan Zemen, Jan Mašek, Vít Novák, Kamil Olejník, et al. Hitachi Cambridge, Univ. Cambridge Jorg Wunderlich, Andrew Irvine, Byonguk Park, et al. Texas A&M Jairo Sinova, et al.
AMR and GMR (TMR) sensors: dawn of spintronics Inductive read elements Magnetoresistive read elements 1980’s-1990’s
Ferromagnetism & spin-orbit coupling anisotropic magnetoresistance Ferromagnetism only giant (tunnel) magnetoresistance ~ 100% MR effect ~ 1% MR effect magnetization current Lord Kelvin 1857 Fert, Grunberg et al. 1988
Renewed interest in SO induced MRs in ferromagnetic semiconductors ~ 1000% MR effect & gate controlled Ohno Science ’98 Coulomb blockade AMR: likely the most sensitive spintronic transistors to date Wunderlich et al. PRL ’06 Coulomb blockade oscillations in (Ga,MnAs) SET as a function of gate voltage and magnetization angle Schlapps et al. arXiv:0904.3225
I B M I V V SO induced MRs: AMR & anomalous 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 B Hall 1879 Hall 1881 V _ M _ _ FSO _ FL I I V Tc in (Ga,Mn)As upto ~190 K but AHE survives and dominates above room-T Ruzmetov et al. PRB ’04
(Ga,Mn)As: simple band structure of the host SC j=3/2 HH HH & LH Fermi surfaces Spherical HH Kohn-Luttinger 3D model Rashba and Dresselhaus 2D models
Intense theory research of AHE in model 2D R&D systems Nagaosa et al RMP ‘’09 in press (arXiv:0904.4154)
Spin-injection Hall effect: SO-induced Hall effect of spin-polarized electrical current injected into non-magnetic system (2DEG) – – – – + + + + + + + + – – – – jqs nonmagnetic Spin-polarizer (e.g. ferromagnet, light) Wunderlich et al. Nature Phys.‘09 - spintronic effect in non-magnetic semiconductors based on SO only immediate prospect for high-T operation - SO-induced Hall effect (like AHE) in the model 2D Rashba&Dresselhaus systems - and more …. - spin-detection tool of unique SO-induced spin dynamics effects in 2D systems - directly applicable to a variety of opto-spintronic, spintronic transitor, etc. devices
Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell p 2DHG i n 9
Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell - p 2DHG i n 10
Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell i p n 2DHG 2DEG 11
Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell h h h h h h VH e e e e e e 2DHG 2DEG
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 1m from the p-n junction safely outside the spin-generation area and/or masked Hall probes
Experimental observation of the SIHE
SIHE linear in degree of polarization and spatially varying
Spin dynamics in Rashba&Dresselhaus SO-couped 2DEG > 0, = 0 = 0, < 0 k-dependent SO field strong precession & spin-decoherence due to scattering
No decoherence for || = || & channel SO field Bernevig et al PRL’06 [110] [1-10]
Diffusive spin dynamics & Hall effect due to skew scattering 18
lacks nano-scale resolution 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
100-10nm resolution with current lithography 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
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 All-electric Datta-Das like transistor with Fe or (Ga,Mn)As spin-injectors, top/bottom gate electrode, and SIHE detection