Evidence for Single-gap Superconductivity in Mg(B1-xCx)2 Single Crystals with x=0.132 from Point-Contact Spectroscopy
Abstract
We report the results of the first directional point-contact measurements in Mg(B1-xCx)2 single crystals with 0.047 <= x <= 0.132. The two-gap superconductivity typical of MgB2 persists up to x=0.105. In this region, the values of the gaps Deltasigma and Deltapi were determined by fitting the Andreev-reflection conductance curves with a two-band Blonder-Tinkham-Klapwijk (BTK) model, and confirmed by the single-band BTK fit of the sigma- and pi-band conductances, separated by means of a magnetic field. At x=0.132, when Tc=19 K, we clearly observed for the first time the merging of the two gaps into one of amplitude Delta~3 meV.
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