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Solid-state physics

U-turns strictly prohibited

Nature volume 466, pages 323–324 (2010)Cite this article

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According to theory, electrons on the surface of a topological insulator are not allowed to make U-turns. This notion, and some of its main consequences, has now been tested experimentally.

The second concept that underlies electron behaviour in helical metals, but that also applies to ordinary metals, is time-reversal symmetry — that is, under a time-reversal transformation, all microscopic physical processes remain unchanged, but are just running backwards. And indeed, the electron configurations in both ordinary and helical metals are invariant under such a transformation: simultaneously reversing the direction of travel (with k going to −k) and the spin orientation of all electrons in the material leaves the energy-band structure of the system unchanged (Fig. 2).

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Figure 1: Electron scattering from point-like and line-like defects.
Figure 2: Energy-band structure and spin orientation in normal and helical metals.

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Authors and Affiliations

  1. Marcel Franz is in the Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada. franz@physics.ubc.ca,

    Marcel Franz

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  1. Marcel Franz
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Franz, M. U-turns strictly prohibited. Nature 466, 323–324 (2010). https://doi.org/10.1038/466323a

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