Spin Transport Goes Ballistic

The circuits in today’s computers, cell-phone cameras, and many other electronic devices rely on the manipulation of electronic charges via CMOS technology—transistors built from a combination of “complementary” metal, oxide, and semiconductor materials. A promising “beyond-CMOS” technology [1] is spintronics, in which information is carried by spin instead of charge. Spintronics devices could consume less power than CMOS devices and enable new applications. But efficiently injecting spins into conducting, two-dimensional channels, such as those that would be used in a spinbased version of the transistor, is difficult because of the large impedance mismatch between the spin “source” (typically a ferromagnet) and the channel, a result of the very different electronic density of states in the two materials. Now, researchers led by Dieter Weiss at the University of Regensburg, Germany, have achieved a high spininjection efficiency from a ferromagnetic metallic semiconductor into the highly conducting two-dimensional electron gas that forms at the interface between two semiconductors [2]. In addition to expanding the types of materials that can be used in spintronics, their experiments reveal spin-transport effects that can’t be explained by existing models, and may open up new ways of thinking about spintronic devices.