Room-Temperature Spin Hall Effect

A new experiment by David Awschalom and his colleagues at the University of California, Santa Barbara, plus collaborators from Pennsylvania State University, shoots a stream of electrons through a sample of a non-magnetic semiconductor, and segregates the electrons in such a way that those with spins pointing up are steered to the left while those with downward pointing spins deflect to the right. They also demonstrated that they could polarize the electrons (orient their spins) using only electric fields at room temperature as well, a great boon for prospective spintronics circuitry that would fashion a new form of electronics in which both charge and spin provide ways of storing and processing data.

Strangely, Awschalom's new results -- showing a spin current all the way up to room temperature -- is conducted not in Gallium Arsenide, where most previous observations of the spin Hall effect have been made, but in Zinc Selenide, which should not be as efficient at electrically polarizing spins.

Awschalom (awsch@physics.ucsb.edu, 805-893-2121) says that the evidence that the spin Hall effect is strong even in a material where it should be weak will kindle further an interesting controversy swirling around interpretations of the spin Hall effect. The new experiment is a spin equivalent of the conventional Hall effect known since the 19th century.

In the old Hall effect electrons, moving longitudinally through a sample under the force of an applied electric field will, if exposed to a vertically oriented magnetic field, be deflected slightly to one side of the sample. Two years ago physicists showed that a kind of Hall effect could be used to steer spins (to be more exact, electrons polarized with spins up or down) so that even while no pileup of electric charges at the edge of the sample would occur a net pileup of spins would occur (see Physics Today, February 2005).

In another recent experiment, Awschalom and colleagues showed that the spins wouldn't just pile up; they could be led off into a wire and constitute a polarized current, where they would be to a spintronic circuit of spin transistors what an ordinary current is to ordinary electronics.

Two articles in Physical Review Letters:
Sih et al., in the 1 September 2006 issue, and
Stern et al. in the 22 September 2006 issue
Contact David Awschalom
University of California, Santa Barbara
Tel: 805-893-2121
awsch@physics.ucsb.edu
The Awschalom Group Web site