Spin Hall effect detected at room temperature
Sep 11, 2006
Physicists in the US are the first to detect the spin Hall effect at room temperature, in what could be an important development in the quest for a practical source of spin-polarized electrons for spintronic devices.
David Awschalom and colleagues at the Center for Spintronics and Computation at the University of California, Santa Barbara observed the current-induced spin-polarization of electrons and the spin Hall effect in thin surface layers of ZnSe.
Observations were made in the 10 to 295K temperature range using Kerr rotation (KR) spectroscopy. The team, which also included researchers from Pennsylvania State University, will report their findings in an upcoming issue of the journal Physical Review Letters.
The spin Hall effect was first observed in GaAs at 20K by Awschalom and Yuichiro Kato in 2004. It consists of a spin current flowing in a transverse direction to the charge current in a non-magnetic material and in the absence of an applied magnetic field. The result is a measurable accumulation of “spin up” and “spin down” electrons at opposite edges of the conducting channel.
The effect could be of use in the growing field of spintronics, in which the intrinsic spin of the electron (in addition to its electrical charge) is exploited in the development of logic devices. The spin Hall effect could provide a source of spin-polarized electrons for injection into semiconductor devices. Such electrons could carry information based on the state (up or down) of their spin polarization.
According to Awschalom, the unique advantage of using the spin Hall effect is that it does not require a magnetic field or magnetic materials to generate and separate spins in the solid state.
In this experiment, the spin Hall effect was observed in thin films (1.5 μm thick) of the semiconductor material ZnSe. At higher temperatures the researchers noticed a reduction in the spin Hall effect, the spin coherence time (how long electron spin states remain coherent) and the spin polarization. The spin polarization at 20K was about ten times stronger than at room temperature and the spin diffusion length decreased from 1.9 to 1.2 μm over the same temperature range.
The researchers are now working on ways to boost the spin polarization to levels where nearly all electrons are polarized. In previous GaAs experiments performed at Santa Barbara, one electron in 10 000 were spin-polarized by the spin Hall effect.
About the author
Darius Nikbin is a science writer at Institute of Physics Publishing in Bristol, UK