Conservation of electron spin information
A step toward spintronics devices using electron spin as an information unit
Graduate School of Engineering / Faculty of Engineering
Dr. Naoyuki Sugimoto at the Correlated Electron Research Group in RIKEN and Professor Naoto Nagaosa at the Department of Applied Physics, the University of Tokyo have discovered that electron spin information in solids is saved in a “hidden” conserved quantity.
It was thought that electron spin information in solids such as semiconductors was lost during scattering on collision with impurities due to “spin-orbit interaction”, which connects the electron orbital motion and its spin. This loss of spin information is a serious problem for the realization of spintronics devices because it requires that the operations of such devices be completed in only a fraction of the time of traditional electronic devices (less than one nanosecond). The research team derived the law of conservation of spin by expressing spin-orbit interaction using a generalization of the concept of magnetic fields. As a result, they found a hidden conserved quantity holding the initial spin information, and a new phenomenon “spin-orbit echo,” which ensures the recovery of the initial electron spin information. Moreover, the team confirmed by numerical modeling that weakening the spin-orbit interaction returns the spin to its original state and enables the recovery of spin information.
This result could lead to the resolution of the major obstacle for the realization of spintronics devices, and may enable the creation of new devices beyond the limits of conventional electronics.
Naoyuki Sugimoto and Nagaosa Naoto,
Science  (2012): [1413-1416], Online Edition: 2012/6/15 (Japan time), doi: 10.1126/science.1217346.