A paper in today's issue of Nature gives a serious boost to the field of spintronics, in which scientists hope to exploit electron spin to create a distinct class of electronics. Current devices operate by transferring packets of electronic charge. But the new paper reveals that it is also possible to pass clouds of electronic spin between two types of semiconductors, p-type and n-type. "The basis of the transistor is the p-n junction," team leader David Awschalom of the University of California at Santa Barbara says. "The implication of these results is that there is no fundamental reason one can't move forward and fabricate spin transistors."
Awschalom and graduate student Irina Malajovich collaborated with Nitin Samarth and his graduate student Joseph Berry at Penn State University to carry out their experiments. They discovered that if they aligned the spins of a group of electrons and then moved them to an adjacent semiconductor using an electric field, the group would retain its spin alignmenteven as the temperature of the materials went up, sometimes to room temperature. In certain semiconductors, they discovered, the spins survived for a long time, creating in effect spin reservoirs for drawing a spin current.
In addition, they uncovered a sort of spin battery, as Michael Roukes of the California Institute of Technology calls it in an accompanying article. "Unexpectedly, if you keep pulling spin from one material to another, the spins in the adjacent layer acquire the original spin frequency and lifetime of the reservoir," Awschalom explains. "Therefore the total transferred spin can have the properties of either the reservoir or the adjacent layer, and an external electric field 'gates' the transition between the two very different regimes." In conclusion, he says, "new discoveries enable new technologies. It's likely the most important applications are yet to be realized."