Paul Crowell of the University of Minnesota in Minneapolis has brought spintronic devices a step nearer by grounding them in a reassuringly familiar landscape: they are the first to develop a simple, all-electric method to both generate and detect spin currents within a standard semiconductor.
In their recent experiment, Crowell and colleagues sent a current through a gallium arsenide semiconductor, doped with silicon impurities and indium to enhance the spin-splitting effect. The impurities were contained within a 2.5-micrometre-deep, 30-micrometre-wide channel: as electrons pinged off the impurities to right or left, they gathered at the channel’s edges, where they passed one of two iron electrodes bordering each side of the channel.
The electron’s spin gives it a tiny magnetic moment, and the moments of the right and left-spinning electrons point in opposite directions. The electrons spinning inside the two iron electrodes only “see” the electrons in the semiconductor that share their alignment – in this case, the right-spinning electrons. Because many of those right-spinning electrons gathered at one side of the semiconductor channel – while left-spinning electrons gather at the other side – one of the iron electrodes sees more negative charge than the other, establishing a voltage between the two and giving the first electrical measurement of the spin Hall effect.