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Science 17 July 2009:
Vol. 325. no. 5938, pp. 278 - 279
DOI: 10.1126/science.1177157
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Perspectives

Physics:

Edge-State Physics Without Magnetic Fields

Markus Büttiker

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.

Department of Theoretical Physics, University of Geneva, 24 Quai E. Ansermet, 1211 Geneva, Switzerland.

E-mail: markus.buttiker{at}unige.ch

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Science. ISSN 0036-8075 (print), 1095-9203 (online)