Point-contact measurements on the carbon-substituted Mg(B1−xCx)2
filament/powder samples directly reveal a retention of the two superconducting
energy gaps in the whole doping range from x=0 to x≈0.1. The
large gap on the σ-band is decreased in an essentially linear fashion
with increasing the carbon concentrations. The changes in the the small gap
Δπ up to 3.8 % C are proportionally smaller and are more difficult
to detect but for the heavily doped sample with x≈0.1 and Tc=22
K both gaps are still present, and significantly reduced, consistent with a
strong essentially linear, reduction of each gap with the transition
temperature.Comment: 5 eps figure