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Topological insulators

The surface surfaces

Nature Nanotechnology volume 7, pages 85–86 (2012)Cite this article

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Circularly polarized light can isolate surface states from bulk states in topological insulators, allowing their unique properties to be probed.

Most materials are either insulators or conductors, and semiconductors straddle the divide by becoming conducting or insulating as their charge-carrier density is tuned. Recently, a new class of materials was discovered that combines these properties in a new way: called topological insulators, they have bulks that are insulating and surfaces that are conducting1,2. Moreover, the spin of their surface electrons is locked in a direction that is perpendicular to the direction of motion (a property known as helicity): this reduces the probability of the electrons being backscattered by surface defects and phonons, thereby lowering the surface resistivity. However, accessing these surface states unambiguously is a challenge, because defects in the bulk increase bulk conductivity, so that any current injected from external electrodes is transported through both surface and bulk states. Now, writing in Nature Nanotechnology, Nuh Gedik of MIT and co-workers have exploited the helicity of surface states to access and control them directly using circularly polarized light, avoiding any significant contribution from bulk conduction3.

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Figure 1: Owing to helicity, circularly polarized light can generate spin-polarized surface current in topological insulators.

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Authors and Affiliations

  1. Judy J. Cha and Yi Cui are in the Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA,

    Judy J. Cha & Yi Cui

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  1. Judy J. Cha
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  2. Yi Cui
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Correspondence to Judy J. Cha or Yi Cui.

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Cha, J., Cui, Y. The surface surfaces. Nature Nanotech 7, 85–86 (2012). https://doi.org/10.1038/nnano.2012.9

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