Evidence for one-gap superconductivity in Mg(B1-xCx)(2) single crystals at x=0.132 by point-contact spectroscopyстатья
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Аннотация:We report the results of directional point-contact measurements in Mg(B1-xCx)(2) single crystals. The amplitudes of the gaps, Delta(pi) and Delta(sigma) were determined for each C content by fitting the experimental low-temperature normalized conductance curves of our "soft" point contacts with the BTK model generalized to the two-band case. We found that, on increasing the carbon content, Delta(sigma) decreases almost linearly with T-c and Delta(pi) slightly increases until, at x = 0.132 (where T-c = 19 K), they assume the same value Delta = 3.2 +/- 0.9 meV. This result is confirmed by the temperature and magnetic-field dependence of the conductance curves at this C content, which do not show any evidence of two distinct gap values. In particular, the A versus T curve follows very well a standard BCS curve, with a gap ratio 2 Delta/k(BTc), = 3.9. These experimental findings are compared to the theoretical predictions of the two-band model in the Eliashberg formulation.