Departmental Colloquium

Optically induced spin, free of charge

John Sipe
Department of Physics and Institute for Optical Sciences, University of Toronto

Time
Wed. November 16, 2005     1:00 PM     Stirling C

Abstract

It has been understood for years that spin polarized currents in semiconductors can be generated by optically injecting spin polarized carriers and then dragging them with a bias voltage. But only recently has it been generally appreciated, and observed experimentally, that spin currents can be optically injected directly. Here the currents appear on the time scale of the injecting pulse or pulses, which typically is on the order of only 100 femtoseconds. Particularly interesting are scenarios where pure spin currents are injected, in which there is no net spin or electrical current generated, but rather there is a "sorting" of injected carriers by their spin, with carriers of one spin sent in one direction and those of the opposite in the other. Strategies for accomplishing this include the quantum interference of one- and two-photon absorption processes across the band gap, and even scenarios involving the use of only a single laser beam. More recent suggestions involve the use of Raman scattering or far infrared absorption in doped semiconductors, and the possibility of generating an AC pure spin current through the excitation of particular superpositions of exciton states. I will review our theoretical calculations of these effects, and some of the experimental results of our collaborators, Professor Henry van Driel at the University of Toronto and Professor Arthur Smirl at the University of Iowa.

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