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Correlation between Superconducting Carrier Density and Transition Temperature in NbB$_{2+x}$

H. Takagiwa·S. Kuroiwa·M. Yamazawa·J. Akimitsu·K. Ohishi·A. Koda·W. Higemoto·R. Kadono
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Abstract

We report on the magnetic penetration depth, lambda, in a type II superconductor NbB_{2+x} determined by muon spin rotation method. We show in the sample with x=0.1 that lambda at 2.0 K is independent of an applied magnetic field. This suggests that the superconducting order parameter in NbB_{2+x} is isotropic, as expected for conventional BCS superconductors. Meanwhile, the superconducting carrier density (proportional to lambda^{-2}) exhibits an interesting tendency of increase with increasing T_c (where T_c varies with x). Possible origin of such behavior is discussed in comparison with the case of exotic superconductors.

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H. Takagiwa, S. Kuroiwa, M. Yamazawa, J. Akimitsu, K. Ohishi, A. Koda, W. Higemoto, R. Kadono. 2004-12-03. Correlation between Superconducting Carrier Density and Transition Temperature in NbB$_{2+x}$. https://doi.org/10.1143/jpsj.74.1386

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