Materials Science

Insensitive Superconductors

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Science  30 Aug 2013:
Vol. 341, Issue 6149, pp. 939
DOI: 10.1126/science.341.6149.939-c

Superconductors are materials that perfectly conduct electricity below a transition temperature Tc, which generally depends on the density of the current carriers. The bilayer of the insulating cuprate compound La2CuO4 and the metal La1.65Sr0.45CuO4 is an unusual system, where superconductivity has been shown to occur in a single copper-oxide plane. Wu et al. studied the dependence of Tc on carrier density in a system in which the Sr content of the doped layer La2-xSrxCuO4, labeled x, was varied in tiny steps. The films were grown by molecular beam epitaxy with a small doping gradient, so that a single film, after lithographic patterning, yielded a combinatorial library of chemical compositions; this technique reduced sample-to-sample variations associated with experimental conditions. The authors measured more than 800 different compositions, covering the range of x from 0.15 to 0.47, and found that Tc remained virtually unchanged; in contrast, the Hall resistance, which reflects carrier density, varied by almost an order of magnitude over the same range. This unusual insensitivity of the transition temperature to carrier density presents a challenge to the theories of superconductivity in interfacial systems.

Nat. Mater. 10.1038/nmat3719 (2013).

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