Transcript Slide 1
Extraordinary magnetoresistance in GaMnAs ohmic and Coulomb blockade devices Tomas Jungwirth Institute of Physics ASCR Alexander Shick, Karel Výborný, Jan Zemen, Vít Novák, Kamil Olejník, et al. Hitachi Cambridge Jorg Wunderlich, Andrew Irvine, David Williams, et al. University of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, Chris King et al. University of Texas and Texas A&M Allan MacDonald, Jairo Sinova University of Wuerzburg Polish Academy of Sciences Laurens Molenkamp, Charles Gould , et al. Tomasz Dietl, et a. Tohoku University Hideo Ohno, et al. GaAs VB GaAs:Mn extrinsic semiconductor Jungwirth et al. arXiv:0707.0665, PRB ’07 in press Mn-acceptor level (IB) GaMnAs disordered VB VB-IB VB-CB Short-range ~ M . s potential - additional Mn-hole binding - ferromagnetism - scattering MIT in p-type GaAs: - shallow acc. (30meV) ~ 1018 cm-3 - Mn (110meV) ~1020 cm-3 Mobilities: - 3-10x larger in GaAs:C - similar in GaAs:Mg or InAs:Mn > 2% Mn: metallic but strongly disordered Mn spacing Model: SO-coupled, exch.-split Bloch VB & disorder - meaningful but difficult for strong disorder - no better than semi-quantitative Anisotropic magnetoresistance EXPERIMENT THEORY Rushforth et al. arXiv:cond-mat/0702357, PRL ’07 in press SO & polarized scatterers Non-crystalline (M vs I) AMR SO & polarized holes anisotropic scattering 10-100x weaker contribution to AMR MnGa ~ mag. only GaMnAs > > scatering amplitudes max AMR add band-warping crystalline (M vs [100]) AMR Spintronic transistor based on AMR type of effect Wunderlich et al. PRL ‘06 Huge, gatable, and hysteretic MR Single-electron transistor Two "gates": electric and magnetic AMR nature of the effect normal AMR Coulomb blockade AMR Spintronic transistor based on CBAMR Source QQind0 = (n+1/2)e Q VD Drain QQ0ind = ne Gate VG eE2/2C C n-1 Q( M ) U dQ'VD ( Q' ) e 0 n n+1 n+2 Q ( Q Q0 ) ( M ) C U & Q0 CG [ VG VM ( M )] &VM 2C e CG [110] F 2 [100] [110] electric & magnetic control of Coulomb blockade oscillations [010] M [010] SO-coupling (M) CBAMR SET • Generic effect in FMs with SO-coupling • Combines electrical transistor action with magnetic storage • Switching between p-type and n-type transistor by M programmable logic Worth trying to look for CBAMR in SO-coupled room-Tc metal FMs • CBAMR if change of |(M)| ~ e2/2C • In our (Ga,Mn)As ~ meV (~ 10 Kelvin) • In room-T ferromagnet change of |(M)|~100K • Room-T conventional SET (e2/2C >300K) possible