Schemes for All-optical Spin Currents

The lifeblood of electronics is the movement of charged objects, usually electrons or holes (places where an electron ought to be but isn't). But besides having mass and charge, electrons possess a magnetic moment, or spin; that is, they behave like little magnets. The use of these spins, independent of charge, might prove to be a valuable commodity for processing information, not least in the area of quantum computing. Indeed, various "spintronic" devices (such as a spin transistor) have already been demonstrated. Can one have a current of spins without also an underlying current of charge? Two physicists at the University of Toronto (Ravi Bhat, 416-978-4364, rbhat@physics.utoronto.ca) propose to do exactly that by illuminating an ensemble of electrons in a semiconductor with light from a pair of laser beams. The light would not only polarize the electrons (orient their spins in space, something which has been done before; see Update 472) but move the electrons around without the need of any applied voltage by manipulating the pattern of interference between the two laser beams. (Bhat and Sipe, Physical Review Letters, 18 December 2000.)