Solid State and Optics Seminar

Wednesday, October 5, 2005

1:00 p.m.

107 Mason Lab

"Imaging the injection, accumulation, and flow of spin-polarized electrons in lateral ferromagnet/semiconductor devices"

Dr. Scott A. Crooker
Los Alamos National Lab

Abstract

Three essential elements of a functional semiconductor spin transport device are 1) an efficient mechanism for electrically injecting spin-polarized electrons, 2) a practical means for spin manipulation and transport, and 3) a simple electronic scheme for detecting the resulting spin polarization. Using methods for scanning magneto-optical Kerr-effect microscopy, we directly image the electrical injection and subsequent transport of spin polarized electrons in lateral ferromagnet/semiconductor devices [1]. These structures have metallic ferromagnetic (Fe) source and drain tunnel-barrier contacts at opposite ends of a lightly-doped n:GaAs semiconductor channel. The images reveal efficient electrical spin injection into the GaAs channel, and accumulation of spin polarized electrons near the drain contact. Both injected and accumulated electrons have the same spin orientation (antiparallel to the contact magnetization). By controlling, in situ, the uniaxial strain applied to the device substrate [2], one can show that the accumulated spin polarization actually flows away from the drain contact (against the net electron current), indicating that these electrons are polarized by reflection from the ferromagnetic drain contact. Furthermore, the electrical conductance of these devices is modulated by the spin orientation of electrons flowing through the drain, demonstrating that the Fe/GaAs tunnel barrier contacts function both as electrical spin injectors as well as detectors.

[1] S.A. Crooker, M. Furis, X. Lou, C. Adelmann, D.L. Smith, C.J. Palmstrom, and P.A. Crowell, to appear in Science.
[2] S.A. Crooker and D.L. Smith, Phys. Rev. Lett. v94, p236601 (2005).
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Host: Jack Harris