Dery and Sham, Phys. Rev. Lett. 98, 046602 (2007)

1. Spin extraction from semiconductor (sc) to ferromagnet (FM) Lu. J. Sham, H. Dery, L. Cywinski, and P. Dalal, University of California San Diego, DMR 0325599 • The magnetic direction of the spin current in the sc may be reversed by electrical means by controlling a gate to the FM/sc junction. • This phenomenon has potentially important application in spintronics circuits such as the one we designed [Nature 447, 573 (2007)], where both information coding and the readout of the spin current in the sc require the rotation of the relative magnetic direction between the FM and the sc. • It provides an alternative means to the FM magnetization reversal by a magnetic field or a large current through the FM. • This property is found through a quantum theory of scattering of electrons by the Schottky barrier including the inelastic process through the bound states at the interface due to the heavy doping to narrow the barrier for efficient spin injection. • It explains the difference in electron spin directions in injection and extraction found by experiments of Crooker et al. [Science 2006] A Spin Switch FM = ferromagnet sc = semiconductor insulator (a) sc metal back gate (b) (c) energy position To the usual ferromagnet/semiconductor Schottky junction, a back gate is added. The current from sc to FM is dominated by the extended electrons at the blue level, producing spin accumulation on the sc side. The back gate renders the bound electrons at the red levels to dominate the current, reversing the direction of the accumulated spins. Dery and Sham, Phys. Rev. Lett. 98, 046602 (2007)

2. Optical Control in Semiconductors for Spintronics and Quantum Information ProcessingLu. J. Sham, University of California-San Diego, DMR-0325599 Societal Impact: Spin control is a basic quantum physics problem. Its application to spintronics requires close collaboration between physicists and engineers, both present in this group. The short-range impact is the training of students and postdocs ready for the challenge of spin, nano and quantum engineering. The long-range impact is a teaching paradigm and the expectation that our theory and designs, be them successes or failures, will stimulate research and industrial development of spintronics to meet the criteria for a competing technology with the current dominant electronics technology. The societal benefits would be enormous. Education: Lukasz Cywinski, graduated with a Ph.D. in July, provided theory for Kono’s group on optical control of ferromagnetism in semiconductor and theory of spin currents for our device design. Hanan Dery, a postdoc now on faculty at Rochester, did the interdisciplinary work of applying spin physics to device and circuits. Parin Dalal, a Ph.D. student with industrial experience and patents, is using information science to design spintronics circuits and to assess the information capacity of ensemble and single spins for spintronics and quantum information processing.