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Quantum Oscillations and Hall Anomaly of Surface States in the Topological Insulator Bi2Te3

Science  13 Aug 2010:
Vol. 329, Issue 5993, pp. 821-824
DOI: 10.1126/science.1189792

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Carrier Mobility in Topological Insulators

In addition to an energy gap, which is a characteristic of all band insulators, the electronic structure of the recently discovered three-dimensional topological insulators Bi2Te3 and Bi2Se3 contains a surface state with a Dirac-like dispersion. This state is predicted to be associated with high carrier mobility. However, the transport properties of the surface state are obscured by the bulk material and challenging to measure. Qu et al. (p. 821, published online 29 July) produced crystals of Bi2Te3 with the Fermi energy lying in the bulk gap and detected quantum oscillations whose magnetic field dependence reveals that they come from a two-dimensional Fermi surface. An anomaly in the Hall conductance originating from the surface state was also observed. The two measurements independently yield mutually consistent high electron mobilities.

Abstract

Topological insulators are insulating materials that display massless, Dirac-like surface states in which the electrons have only one spin degree of freedom on each surface. These states have been imaged by photoemission, but little information on their transport parameters, for example, mobility, is available. We report the observation of Shubnikov–de Haas oscillations arising from the surface states in nonmetallic crystals of Bi2Te3. In addition, we uncovered a Hall anomaly in weak fields, which enables the surface current to be seen directly. Both experiments yield a surface mobility (9000 to 10,000 centimeter2 per volt-second) that is substantially higher than in the bulk. The Fermi velocity of 4 × 105 meters per second obtained from these transport experiments agrees with angle-resolved photoemission experiments.

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