Direct Measurement of Electron Spins in a Topological Insulator

*Note: This news was first mentioned in the June 2011 issue of Nanotech Japan Update*

Tohoku University, Osaka University and Japan Science and Technology Agency (JST) announced on May 17, 2011 that researchers of Tohoku University and Osaka University jointly succeeded in di-rectly observing electron spins in a topological insulator. The work has been supported by JST and published in Physical Review Letters with the lead author Seigo Souma, Assistant Professor of Tohoku University.

The charge of electron has been a basic carrier of information. However, another entity of electron, i.e. spin, is also expected to be an information carrier in the next generation systems. Topological insu-lator is a promising material recently recognized for the working spin, or a material for spintronics since its “edge” (e.g. surface on a bulk material) serves as a conducting path depending on the spin pola-rization. Direct observation of spin states will be a key step to control electron spins in the material.

Researchers have performed spin-resolved photoemission spectroscopy of a topological insulator Bi2Te3 and present the first direct evidence for the existence of the out-of-plane spin component on the surface state. The magnitude of the out-of-plane spin polarization reaches maximally 25% of the in-plane counterpart. Its existence is presumed to come from the hexagonally deformed Fermi surface in momentum space, since no out-of-plane spin component is observed in another topological insulator TlBiSe2 with circular Fermi surface.

Although a problem remains in the quantitative difference from theoretical prediction, researchers stated that the direct measurement of electron spins is a remarkable step toward a next-generation energy conservation device.

Journal information

S. Souma, K. Kosaka, T. Sato, M. Komatsu, A. Takayama, T. Takahashi, M. Kriener, Kouji Segawa, and Yoichi Ando, “Direct measurement of the out-of-plane spin texture in the Dirac-cone surface state of a topological insulator”, Physical Review Letters, Vol. 21, No. 12, pp. 216803 (2011) [4 pages] Published May 25, 2011