Systematic study of the two band/two gap superconductivity in carbon-substituted MgB2 by point-contact spectroscopy

Abstract

Point-contact measurements on the carbon-substituted Mg(B${}_{1-x}$C${}_x$)${}_2$ filament/powder samples directly reveal a retention of the two superconducting energy gaps in the whole doping range from $x=0$ to $x\approx 0.1$. The large gap on the $\sigma$-band is decreased in an essentially linear fashion with increasing the carbon concentrations. The changes in the the small gap ${\Delta }_{\pi }$ up to 3.8 % C are proportionally smaller and are more difficult to detect but for the heavily doped sample with $x\approx 0.1$ and $T_c=22$ K both gaps are still present, and significantly reduced, consistent with a strong essentially linear, reduction of each gap with the transition temperature.

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