A Very Thin Superconductor

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Science  17 Jan 2014:
Vol. 343, Issue 6168, pp. 231
DOI: 10.1126/science.343.6168.231-c

Manipulating the dimensionality of materials can lead to profound changes in their electronic properties. The iron-based superconductor FeSe has a relatively low superconducting transition temperature Tc of about 8 K in the bulk; however, spectroscopic measurements have suggested that a single-unit-cell layer of this material has a much higher Tc. Transport measurements needed to confirm this finding proved challenging; now, Zhang et al. overcome these difficulties by growing the FeSe layer on a SrTiO3 substrate and capping it with FeTe, with an additional layer of Si deposited on top of the FeTe to prevent its exposure to air. By measuring the electrical resistance as a function of temperature, they detected the onset of superconductivity at a temperature higher than 40 K; the critical current density, important for practical applications, was much higher than in the bulk. Because neither the substrate nor the capping layer exhibited superconductivity, and the transport characteristics power laws were consistent with the Berezinskii-Kosterlitz-Thouless transition, the superconductivity appears to be a genuine property of the FeSe layer and has a two-dimensional nature. Because of its relative simplicity, the system presents a good testing ground for unconventional superconductivity.

Chin. Phys. Lett. 31, 017401 (2014).

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