delocalized

1. Nuclear enhancement of the spin Hall angle near the metal-insulator transition in n-GaAs Hall current: flow indicies C. C. Geppert1, K. D. Christie1 , M. K. Chan1, Q. O. Hu2, S. J. Patel2, C. J. Palmstrøm2, 3, P. A. Crowell1 orientation 1School of Physics and Astronomy, University of Minnesota, U.S.A. 2Dept. of Electrical and Computer Engineering, 3Dept. of Materials, University of California Santa Barbara, U.S.A. Transport skewess: Cap (5 nm) Fe n:GaAs n~ 5 x 1018 cm-3 (15 nm) Tunnel barrier nn+:GaAsn+~ 5 x 1018 cm-3 (15 nm) n:GaAs n~ 5 x 1016 cm-3 (~ 2500 nm) A large Hanle signal is observed in the local Hall voltage when injecting vertical spin currents from a central ferromagnetic contact. This inverse spin Hall effect (ISHE) is caused by an asymmetry in the scattering for spin-up and spin-down electrons. Add description here about the metal-insulator transition. Fix the atrocious DOS diagrams below. Prune as necessary. V Semi-insulating GaAs substrate [001] localized delocalized The observed signal is even (odd) with respect to the applied field in samples with the contact magnetization oriented perpendicular (parallel) to the Hall arms. Preliminary doping dependence studies indicate that the ISHE signal does pass through a resonance as a function of doping. The curves below are plotted such that the displayed magnitude corresponds to the same injected spin polarization for all three samples as measured by companion non-local devices. The low temperature conductivity can be fit well by The signal collapses near zero-field unlike the electron spin polarization which is at a maximum. The signal magnitude is much larger than expectations based on ionized impurity scattering. A large nuclear magnetic resonance (NMR) response is observed in the Hall voltage. determined from fit is much less than hydrogenic donor binding energy (). • electron spin splitting • spin-orbit coupling • Overhauser field Expected lineshape: Estimating of states are localized compares nicely to from Hertz distribution ( localization criterion). even Hanle curve (quasi-Lorentzian) Nuclear Origin Phenomenological Modeling Introduction Resonant Scattering Local Moments Summary Quantum corrections due to electron-electron interactions () very sensitive to application of an electric field. Garlid et. al., PRL 105, 156602 (2010) The presence of neutral impurity scattering can be clearly seen in the bias dependence of the channel conductivity. Donor impact ionization becomes less effective at higher carrier concentrations. MIT: exchange splitting in band metallic insulating Plotting the ISHE signal vs. the magnitude of the spin polarization (non-local spin valve) exhibits a clear super-linear behavior. To manipulate the nuclear spin system independently of the electron spin polarization, we employ a pump-probe technique to take advantage of the large separation in relaxation time scales. y x In the absence of nuclear polarization, the ISHE signal is completely extinguished, whereas the electron spin polarization (3T) actually increases due to the smaller effective Overhauser field. probe bias quasi-particle peak pump bias slope density of states for spin . density of states for spin . One advantage of this technique is the ability to take field sweeps with the nuclear polarization in steady-state. The graph on the left shows the component of the ISHE signal which is odd with respect to the contact magnetization. While it is well known that the electron precession dynamics see the nuclei as an effective field, this result suggests that the nuclei play a more direct role in the scattering mechanism. Explain here what gamma is and how to calculate it from the scattering amplitudes. Show the origin of the two contributions (1) exchange scattering and (2) Kondo-like flip-flop with the nuclear system. • By solving self-consistently the 3D spin drift-diffusion model including nuclear and fringe fields, the spin current tensor can be determined at each cell. Calculating the corresponding anomalous current yields excellent qualitative agreement with the ISHE line-shapes over a wide variety of angles, transverse fields, and nuclear parameters. Both contributions present: