Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 57: Focused Session: Spin-Orbit Interaction at Surfafces: From the Rashba Effect to Topological States of Matter II

O 57.2: Topical Talk

Donnerstag, 26. März 2009, 15:30–16:00, HSZ 02

Quantum spin Hall phases and topological surface states — •Shuichi Murakami — Department of Physics, Tokyo Institute of Technology, Tokyo, Japan — PRESTO, JST

Triggered by the research of the spin Hall effect [1], quantum spin Hall (QSH) effect [2,3] is studied intensively in recent years. The QSH system is an insulator in the bulk, while the boundary (i.e. edge in 2D and surface in 3D) supports gapless states carrying spin currents due to spin-orbit coupling. These edge or surface states remain gapless, and are robust against nonmagnetic impurities and surface roughness. This robustness stems from bulk topological order characterized by the Z₂ topological number. Namely, the bulk topological properties become manifest as an existence of the gapless boundary states.

The QSH effect occurs under a zero magnetic field unlike the quantum Hall effect. In some materials this effect occurs in nature without applying fields, as demonstrated theoretically and experimentally. In my talk I explain our theoretical proposal that the (111)1-bilayer bismuth ultrathin film shows the QSH effect [4]. I also discuss strategies to search for candidate materials showing the QSH effect.

[1] S. Murakami, N. Nagaosa, and S.-C. Zhang, Science 301, 1348 (2003). [2] C. L. Kane and E. J. Mele, Phys. Rev. Lett. 95, 146802; ibid. 95, 226801 (2005). [3] B. A. Bernevig and S.-C. Zhang, Phys. Rev. Lett.96.106802 (2006). [4] S. Murakami, Phys. Rev. Lett. 97, 236805 (2006).