Transcript Slide 1
From ferromagnetic to non-magnetic semiconductor spintronics: Spin-injection Hall effect Tomas Jungwirth Institute of Physics ASCR Karel Výborný, Jan Zemen, Jan Mašek, Vít Novák, Kamil Olejník, et al. University of Nottingham Bryan Gallagher, Richard Campion, Kevin Edmonds, Andrew Rushforth, 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 ~ 1% MR effect Ferromagnetism only giant (tunnel) magnetoresistance ~ 100% 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 Schlapps et al. arXiv:0904.3225 Coulomb blockade oscillations in (Ga,MnAs) SET as a function of gate voltage and magnetization angle 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 Hall 1879 Hall 1881 B _ M FL __ I I V FSO 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) ++++ –––– –––– ++++ Spin-polarizer (e.g. ferromagnet, light) jqs nonmagnetic 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 ni p 2DHG 9 Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell - ni p 2DHG 10 Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell p i 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 e VH e e e e e 2DHG 2DEG Optical spin-generation area near the p-n junction Simulated band-profile Vb h h h h h h e e e e e VL e VH2 2DHG 2DEG 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 H 2DEG 2k 2 k y x k x y k x x k y y 2m > 0, = 0 = 0, < 0 k-dependent SO field strong precession & spin-decoherence due to scattering No decoherence for || = || & channel SO field L[110 ] k[110 ]t / m 4k[110 ]t / Bernevig et al PRL’06 [110] [1-10] Diffusive spin dynamics & Hall effect due to skew scattering 2k 2 * H 2DEG k y x k x y k x x k y y (k Vdis (r )) 2m H ( x[1 1 0] ) 2 * pZ ( x[1 1 0] ) exp[q x[1 1 0] ] ~2~ 2 ~ 4 q | q | exp(i ) , | q | ( L1 L2 L2 )1 4 L~ 2 L~ 2 L~ 4 4 12 arctan ~1 2 2 ~ 2 1 L L 2 2 1 ~ L1/ 2 2m | | 2 e n pz ( x[1 1 0] ) ni SIHE vs other spin-detection tools in semiconductors Crooker et al. JAP’07, others Magneto-optical imaging non-destructive lacks nano-scale resolution and only an optical lab tool MR Ferromagnet electrical requires semiconductor/magnet Ohno et al. Nature’99, others hybrid design & B-field to orient the FM spin-LED all-semiconductor requires further conversion of emitted light to electrical signal 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