PerspectivePhysics

Cuprates Get Orders to Charge

Science  17 Aug 2012:
Vol. 337, Issue 6096, pp. 811-812
DOI: 10.1126/science.1227082

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Summary

A quarter century after their initial discovery, copper oxide high-temperature superconductors (HTSs) continue to fascinate and frustrate researchers. One of the big challenges to understanding these materials is that the standard model of electron motion in solids—the same model that had to be developed before Bardeen, Cooper, and Schrieffer could formulate their theory of superconductivity in 1957—does not apply, and no convenient replacement is yet in sight. While theoretical efforts proceed, the focus of research has periodically shifted from one experimental surprise to another. For example, several years ago it was discovered in the superconducting compound YBa2Cu3O6+x that when the superconducting order is suppressed by a very strong magnetic field, various electronic responses oscillate with the field strength in a way that indicates the presence of a new electronic ordering (1, 2). These experiments stimulated a great deal of theoretical excitement, but a compelling explanation has been lacking. On page 821 of this issue, Ghiringhelli et al. (3) report the experimental observation of a specific charge ordering more complicated than generally imagined. Together with an independent study of this order in a magnetic field (4), an explanation for the quantum oscillation experiments appears to be at hand. At the same time, these results yield new puzzles.