Physicists at JILA are using ultrashort pulses of laser light to reveal precisely why some electrons, like ballet dancers, hold their spin positions better than others—work that may help improve spintronic devices, which exploit the magnetism or “spin” of electrons in addition to or instead of their charge. One thing spinning electrons like, it turns out, is some disorder.
JILA is a joint venture of the National Institute of Standards and Technology and the University of Colorado at Boulder.
Electrons act like tiny bar magnets whose poles can point up or down. So-called "spintronic" circuits that sense changes in electron spin already are used in very high-density data storage devices, and other spin-based devices are under study. Greater exploitation of spintronics will require spins to be stable—in this case meaning that electrons can maintain their spin states for perhaps tens of nanoseconds while also traveling microscale distances through electronic circuits or between devices.
Scientists have suspected for some time that electrons best maintain the same spin direction at a "magic" electron density. New JILA measurements, described in Nature Physics, suggest where the magic originates, revealing that electrons actually hold their spins for the longest time—three nanoseconds—when confined around defects, or disordered areas, in semiconductors.
They lose their spin alignment in just a few hundred picoseconds when flowing through perfect areas of the crystal. This finding explains the role of density: at very low density, electrons are strongly confined to different local environments, whereas at extremely high density, electrons start hitting each other and lose spin control very fast. The magic point of maximum spin memory occurs at the cross-over between these two conditions.