A “spin battery”

Has been demonstrated by researchers at the University of California, Santa Barbara, and Pennsylvania State University. They have shown that a persistent coherent spin current can flow across an interface between two n-doped semiconductor materials, at a temperature of 5 K. The discovery is a positive step in the quest for spintronic semiconductor devices that manipulate electron spins rather than charges. (See the article by David D. Awschalom and James M. Kikkawa in Physics Today June 1999, page 33 .) Putting an external electric field across the interface between a gallium arsenide spin reservoir and a zinc selenide layer increased the efficiency of spin transfer by a factor of 5 over that with no electrical bias. The characteristics of the spin signal in the ZnSe layer were surprisingly representative of the spin properties of the GaAs layer. When the same team replaced the n-doped GaAs reservoir with p-doped GaAs, they found up to 40 times greater efficiency of spin transfer, facilitated by the internal field at the p–n interface. The findings show promise for multifunctional spintronic devices, such as spin transistors, in which the amplitude and phase of a coherent spin current can be controlled by either electric or magnetic fields. (I. Malajovich, J. J. Berry, N. Samarth, D. D. Awschalom, Nature 411 , 770, 2001 http://dx.doi.org/10.1038/35081014 .)