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Physics of spin current - Spin Hall effect and quantum spin Hall effect

Speaker:Prof. Shuichi Murakami
Affiliation:Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
Date:May 21, 2009 (Thu)
Time:4:00-5:30 p.m.
Venue:Lecture Theatre P4, Chong Yuet Ming Physics Building, HKU


Physics of spin current is a new field of research in solid state physics. The spin current is invariant under time reversal, unlike the spin itself, and hence can be induced without a magnetic field or a magnet. In my talk I discuss our works on two subjects of the spin-current physics: the spin Hall effect and the quantum spin Hall effect.


The spin Hall effect is an effect of inducing a transverse spin current by an electric field in a metal or in a doped semiconductor. This effect can be induced by the "Berry phase in k-space", i.e. the geometric structure of the band structure of the solid itself. In my talk I explain how this mechanism works in various systems, for example in p-type semiconductors and in platinum. The quantum spin Hall (QSH) effect is closely related to the spin Hall effect, but it occurs in insulators. In the systems showing the QSH effect, the bulk is gapped and insulating, while there are gapless states on the edge (in 2D) or on the surface (in 3D) carrying a spin current. We discuss what kind of insulators can show this effect, and explain our recent theoretical proposal that bismuth ultrathin film shows the QSH effect.


About the Speaker:

Shuichi Murakami obtained his PhD in 1999 at the University of Tokyo, Japan. He has been one of the most active researchers in the field of spintronics. He developed the theory of spin Hall effect and his paper in Science (2003) represents one of the pioneering works in spin Hall effect, which has received citation of over 600.



Physics colloquium series is organized to introduce cutting edge researches and new development in physics, designed to be suitable to graduate and undergraduate students, and also to scientists working on different fields. Each colloquium will generally start with an extensive introduction of the background of the field, followed by forefront research topics and results. The colloquium will serve as an education forum for students and laymen alike, and also serve as a platform for exchange and update their knowledge of various branches of physics among academic staff members.