Room-temperature spin Hall effect

In the regular Hall effect, electrons that move longitudinally under the force of an applied electric field through a sample will, if exposed to a vertically oriented magnetic field, be deflected slightly to one side. Two years ago, physicists showed that a kind of Hall effect in a vertical electric field could produce a net pileup of spins at the edge of the sample, even though no pileup of electric charges would occur (see Physics Today, February 2005, page 17 ). Physicists at the University of California, Santa Barbara, with collaborators from the Pennsylvania State University, now have used a sample of zinc selenide—a nonmagnetic II–VI semiconductor—to demonstrate both electrically induced spin polarization and the segregation of electrons based on spin. Using a diagnostic technique called Kerr rotation spectroscopy, the researchers showed that spins of opposite sign congregated on opposites sides of the sample, that the effect persists all the way up to room temperature, and that no internal magnetic fields arose in the process. All this despite the fact that ZnSe should not be efficient at electrically polarizing spins. Group leader David Awschalom says that the evidence for a strong spin Hall effect in ZnSe will add to the interesting controversy swirling around interpretations of the spin Hall effect. In another recent experiment, Awschalom and colleagues showed that spins needn’t just pile up in a semiconductor; they can be led off as a polarized current into a wire made of the same material. (V. Sih et al., Phys. Rev. Lett. 97 , 096605, 2006 http://dx.doi.org/10.1103/PhysRevLett.97.096605 ; N. P. Stern et al., Phys. Rev. Lett. 97 , 126603, 2006 http://dx.doi.org/10.1103/PhysRevLett.97.126603 .)