SemiSpinNe t Research fueled by: ASRC Workshop on Magnetic Materials and Nanostructures Tokai, Japan January 10 th, 2012 Vivek Amin, JAIRO SINOVA Texas A&M University Institute of Physics ASCR Hitachi Cambridge Joerg W ü nderlich, Andrew Irvine, et al Institute of Physics ASCR Kamil Olejnik, Tomas Jungwirth, Vít Novák, et al University of Nottingham Tomas Jungwirth, Richard Campion, et al. Spin-Hall field effect transistors

2 Nanoelectronics, spintronics, and materials control by spin-orbit coupling I. Optical injection spin-Hall FET Spin based FET: old and new paradigm in charge-spin transport Theory expectations and modeling Experimental results Spin-current AND-gate II. Spin Hall and non-local spin valve detection of electrically injected and manipulated spins: Spin amplifier and modulator non-local spin accumulation measurements Device and key issues Modeling III. Summary spin-Hall field effect transistors

3 Spin-orbit coupling interaction (one of the few echoes of relativistic physics in the solid state) This gives an effective interaction with the electron’s magnetic moment Consequences Effective quantization axis of the spin depends on the momentum of the electron. Band structure (group velocities, scattering rates, etc.) mixed strongly in multi-band systems If treated as scattering the electron gets asymmetrically scattered to the left or to the right depending on its “spin” Classical explanation (in reality it is quantum mechanics + relativity ) “Impurity” potential V(r) Produces an electric field ∇V∇V B eff p s In the rest frame of an electron the electric field generates and effective magnetic field Motion of an electron

4 Problem: Rashba SO coupling in the Datta-Das SFET is used for manipulation of spin (precession) BUT it dephases the spin too quickly (DP mechanism). From DD-FET to new paradigm using SO coupling 1) Can we use SO coupling to manipulate spin AND increase spin-coherence? Can we detect the spin in a non-destructive way electrically? 3) Can this effect be exploited to create a spin-FET logic device? Use the persistent spin-Helix state or quasi-1D-spin channels and control of SO coupling strength (Bernevig et al 06, Weber et al 07, Wünderlich et al 09, Zarbo et al 10) Use AHE to measure injected current polarization electrically (Wünderlich, et al Nature Physics. 09, PRL 04) Spin-Hall AND-gate device (Wünderlich, Jungwirth, et al Science 2010) DD-FET

5 Spin-dynamics in 2D electron gas with Rashba and Dresselhauss SO coupling a 2DEG is well described by the effective Hamiltonian: For our 2DEG system: Hence α ≈ -β Something interesting occurs when [110] _  = 0,  < 0 [110] _ k y [010] k x [100]  > 0,  = 0 1) Can we use SO coupling to manipulate spin AND increase spin-coherence?

6 Local spin-polarization → calculation of AHE signal Weak SO coupling regime → extrinsic skew-scattering term is dominant Lower bound estimate Spin-injection Hall effect: theoretical expectations 1) Can we use SO coupling to manipulate spin AND increase spin-coherence? Can we detect the spin in a non-destructive way electrically? Use the persistent spin-Helix state or 1D-spin channels and control of SO coupling strength Use AHE to measure injected current polarization electrically ✓ ✓

7 Spin-injection Hall device measurements trans. signal σoσoσoσo σ+σ+σ+σ+ σ-σ-σ-σ- σoσoσoσo VLVL SIHE ↔ Anomalous Hall Wunderlich, Irvine, Sinova, Jungwirth, et al, Nature Physics 09

8 T = 250K Further experimental tests of the observed SIHE

9 V H2 I VbVb V H1 x V H2 VbVb V H1 x (a) (b) Spin injection Hall effect Wunderlich, et al, Science 2010 SiHE inverse SHE

Spin-FET with two gates → logic AND function Wunderlich et al., Science.‘10 SHE transistor AND gate

11 Nanoelectronics, spintronics, and materials control by spin-orbit coupling I. Optical injection spin-helix and spin-Hall FET Spin based FET: old and new paradigm in charge-spin transport Theory expectations and modeling Experimental results Spin-current AND-gate II. Spin Hall and non-local spin valve detection of electrically injected and manipulated spins: Spin amplifier and modulator non-local spin accumulation measurements Device and key issues Modeling III. Summary spin-Hall field effect transistors

+ – IDID + – Electrical injection, manipulation, and detection of spins in semiconductors Electrical injection spin-amplifier (modulator) in Fe/GaAs(3D) FM injection from a FM detection of spin current by iSHE detection of spin polarization by FM electrical manipulation of the spin profile by a drift current Huang et al 07

Experimental device set-up IBIB IDID Fe Au V SH V NL n-GaAs Note: I D reminiscent of base current in the bipolar transistor amplifier I B ↔ emitter current detected spin polarization (current) ↔ collector current

14 Electrical non-local spin valve detection by FM and by iSHE Electrical injection of a diffusive spin current from FM into a non-magnetic metal Valenzuela, S. O. & Tinkham, M, Nature‘06 iSHENL spin detection

Valenzuela, S. O. & Tinkham, M, Nature‘06 x y z BzBz Electrical non-local spin valve detection by FM and by iSHE Electrical injection of a diffusive spin current from FM into a non-magnetic metal iSHE NL spin detection

16 high-resitive semiconducor low-resistive FM metal Lou et al. Nature Phys.’07, Ciorga et al. PRB 09, Awo-Affouda et al. APL 09, Salis et al. PRB 09 Fe/n-GaAs Schottky tunnel contacts very high-resitive spin-dependent tunnel contact ↓ Electrical non-local spin valve detection by FM and by iSHE Electrical injection of a diffusive spin current from FM into a non-magnetic semiconductors

17 high-resitive semiconducor low-resistive FM metal Lou et al. Nature Phys.’07, Ciorga et al. PRB 09, Awo-Affouda et al. APL 09, Salis et al. PRB 09 Fe/n-GaAs Schottky tunnel contacts... and by iSHE ? very high-resitive spin-dependent tunnel contact ↓ Electrical non-local spin valve detection by FM and by iSHE Electrical injection of a diffusive spin current from FM into a non-magnetic semiconductors

n-GaAs Fe Al x y z x y z BzBz Key is to experimentally remove the strong ordinary Hall effect in SCs

n-GaAs Al BXBX x y z x y z Fe Key is to experimentally remove the strong ordinary Hall effect in SCs Hanle + iSHE

B aniso  200 mT >> B Hanle  50 mT BXBX x y z x Epitaxial 2 nm Fe on n-GaAs grown in one MBE → large [110]/[1-10] in-plane anisotropy

Plus we know when each Fe electrode switches for a given  B B x y z

(ordinary Hall) BXBX x y z x iSHE Hanle iSHE

Easy-axis switching NL spin-valve Hanle iSHE Hard-axis Hanle NL spin-valve

Nuclear (Overhauser) field: x y z BzBz BXBX x y z B z,aniso  2 T B x,aniso  200 mT Hanle curves affected by nuclear fields

iSHE reverses sign upon reversing spin-current

Electrical spin modulator B x =0

Drift-diffusion equations 1. s y continuous at x=0 2. independent of v d (x) B x =0

Drift velocities Diffusion constant Spin lifetime B x =0 Overall magnitude ( source term )

Theory Experiment

Spin current Hall sensitivity function for a finite-size cross iSHE voltage (~ skew scattering Hall angle in GaAs) SHE analysis from calibrated spin-current

TheoryExperiment

Theory skew scattering Hall angle in GaAs: Theory - experiment comparison Summary of theory DD-equation with non-constant v d analysis Spin-lifetime from out of plane Hanle Fit of DD to NL yields polarization at injection FM electrode Use this injected spin-current estimate to calculate predicted spin Hall angle (because of geometry one needs to calculate the sensitivity function for the Hall cross bar).

34 Summary of spin-injection Hall FET  Basic studies of spin-charge dynamics and Hall effect in non-magnetic systems with SO coupling  Spin-photovoltaic cell: solid state polarimeter on a semiconductor chip requiring no magnetic elements, external magnetic field, or bias  SIHE can be tuned electrically by external gate (e.g. Fe/Ga(Mn)As structures)  Spin amplifier-modulator based on drift current  iSHE and NL in semiconductor device  Strongest theory-experiment comparison to date in SC optical-spin-injection Hall FET all electrical Hall FET