清洁能源中心&表面室学术报告

报告题目： Nanoscale ballistic spin and charge transport in semiconductors studied by optical techniques
报 告 人： Prof. Hui Zhao
Department of Physics and Astronomy, University of Kansas, USA

报告人简介：
Professor Hui Zhao obtained his Ph.D. in 2000 from Beijing Jiaotong University. After that, he spent two years at University of Karlsruhe in Germany as a postdoc in Prof. Kalt’s group. In 2003, he moved to University of Iowa in USA as a postdoc in Prof. Smirl’s group. There, he developed optical pump-probe techniques with ultrahigh spatial resolution of less than 1 nm. Using these techniques, he observed, for the first time, the inverse spin Hall effect, and achieved real-space observation of ballistic pure spin transport. In 2007, he was appointed as an assistant professor at University of Kansas. Currently, he is working on developing novel ultrafast laser techniques and applying them to study nanoscale semiconductor electronics and spintronics. He has more than 50 papers published including 12 papers on PRL, PRB and APL, and more than 10 invitations to colloquia and seminars. He is a referee for more than 10 journals including PRL, PRB, APL, and JAP. More information about his research group can be found at http://people.ku.edu/~huizhao.

Abstract：
Ballistic transport of electrons nanoscales is a fundamental process for semiconductor nano-electronics and nano-spintronics. This talk is on real-space observations of ballistic spin and charge transport and spin Hall effect in GaAs studied by ultrafast optical coherent-control and pump-probe techniques. Some basic ideas of optical injection of ballistic spin and charge currents through quantum interference of multiple absorption pathways will be discussed, followed by an introduction of optical pump-probe techniques and their applications in detecting nanoscale motion of electrons in semiconductors. Using these techniques, the ultrafast evolution of ballistic pure spin currents, pure charge currents and spin-polarized charge currents are directly observed in real space with 200 fs temporal and 1 nm spatial resolutions. Finally, applications of these techniques to study both the ordinary and the inverse spin Hall effects in the ballistic regime will be discussed.