Superconducting energy gap in MgCNi3 single crystals: Point-contact   spectroscopy and specific-heat measurements
  Specific heat has been measured down to 600 mK and up to 8 Tesla by the highly sensitive AC microcalorimetry on the MgCNi3 single crystals with Tc ~ 7 K. Exponential decay of the electronic specific heat at low temperatures proved that a superconducting energy gap is fully open on the whole Fermi surface, in agreement with our previous magnetic penetration depth measurements on the same crystals. The specific-heat data analysis shows consistently the strong coupling strength 2D/kTc ~ 4. This scenario is supported by the direct gap measurements via the point-contact spectroscopy. Moreover, the spectroscopy measurements show a decrease in the critical temperature at the sample surface accounting for the observed differences of the superfluid density deduced from the measurements by different techniques. 
Z. Pribulova, J. Kacmarcik, C. Marcenat, P. Szabo, T. Klein, A.   Demuer, P. Rodiere, D. J. Jang, H. S. Lee, H. G. Lee, S.-I...
cond-mat.supr-con