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

TL;DR

This study investigates how carbon doping affects the two-gap superconductivity in MgB2, revealing that both gaps decrease linearly with increasing carbon content while maintaining their two-gap structure.

Contribution

It provides the first systematic experimental evidence that two-gap superconductivity persists in MgB2 with up to 10% carbon substitution, with gaps decreasing linearly.

Findings

Both superconducting gaps decrease linearly with carbon doping.

Two-gap structure remains present up to 10% carbon substitution.

Superconducting transition temperature correlates linearly with gap reduction.

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.