Two band/two gap superconductivity in carbon-substituted MgB2 evidenced by point-contact spectroscopy

The Andreev reflection measurements of the superconducting energy gap in the carbon-substituted MgB${}_2$ are presented. Despite the strong suppression of the transition temperature by 17 K in comparison with the pure MgB${}_2$, the same reduced value of the small superconducting energy gap with $2\Delta/kT_c \approx$ 1.7 has been systematically observed. This indicates that the two band/two gap superconductivity is still preserved here.