How Do You Want That Insulator?

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Science  29 Apr 2011:
Vol. 332, Issue 6029, pp. 546-547
DOI: 10.1126/science.1205251

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An expert chef can take ordinary foods and bring out extraordinary flavors and textures, usually through a combination of the right ingredients and exacting cooking techniques. If the electrical conductivity of a material can be thought of as the flavor of a dish, nature can serve up specialties, such as ceramic insulators that become superconductors when served cold and when the ingredients (the chemical components) are carefully tuned. Superconductivity is an example of an emergent quantum phenomenon—one that is created by the coordinated motion of many particles (1). On page 560 of this issue, Xu et al. (2) report how tuning the composition of normal insulators can turn them into topological insulators, which are another example of materials exhibiting emergent quantum phenomena (35). This result has important implications for the promise of topological insulators in lower-power devices that rely on electron spin rather than charge.