Edge-State Physics Without Magnetic Fields

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Science  17 Jul 2009:
Vol. 325, Issue 5938, pp. 278-279
DOI: 10.1126/science.1177157

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Solids can be divided into conductors and insulators. A new class of materials, called topological insulators, has been predicted (1, 2) that exhibit surface states that lead to quantized conductance of charge and spin. These surface states are helical edge states, which interconnect spin and momentum of the carriers. Observation of these states should not require application of a magnetic field. On page 294 of this issue, Roth et al. (3) present compelling experimental evidence for such helical edge states at the surface of a topological insulator—in this case, quantum wells of mercury telluride (HgTe). Related effects are seen in the quantum Hall effect, but only in the presence of high magnetic fields. In the quantum Hall effect, a magnetic field induces cyclotron motion of electrons that is essential for the formation of edge states.