Extreme Sensitivity of Superconductivity to Stoichiometry in Fe1+δ Se
The recently discovered iron arsenide superconductors appear to display a universal set of characteristic features, including proximity to a magnetically ordered state and robustness of the superconductivity in the presence of disorder. Here we show that superconductivity in Fe1+δ Se, which can be considered the parent compound of the superconducting arsenide family, is destroyed by very small changes in stoichiometry. Further, we show that nonsuperconducting Fe1+δ Se is not magnetically ordered down to 5 K. These results suggest that robust superconductivity and immediate instability against an ordered magnetic state should not be considered as intrinsic characteristics of iron-based superconducting systems.
T. M. McQueen and Q. Huang and V. G. Ksenofontov and C. Felser and Q. Xu and H. W. Zandbergen and Y. S. Hor and J. M. Allred and A. J. Williams and D. Qu and J. G. Checkelsky and N. Ong and R. J. Cava, "Extreme Sensitivity of Superconductivity to Stoichiometry in Fe1+δ Se," Physical Review B - Condensed Matter and Materials Physics, vol. 79, no. 1, American Physical Society (APS), Jan 2009.
The definitive version is available at http://dx.doi.org/10.1103/PhysRevB.79.014522
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