MgCNi3 : Complex behavior in a strongly coupled superconductor

Polycrystalline samples of the recently discovered MgCNi3 superconductor were investigated by transport, ac susceptibility, dc magnetization and specific heat measurements in magnetic fields up to 16 T. Consistent results were obtained for the temperature dependence of the upper critical field H_c2(T) from resistance, ac susceptibility and specific heat measurements. A WHH like temperature dependence of H_c2(T) and the quadratic relationship H_c2(0) ~ T_c^2 point to an effective predominant single band behavior near the quasi clean limit. Evidence for strong electron-phonon and electron-paramagnon coupling was found analyzing the specific heat data. The corresponding s- and p-wave scenarios are briefly discussed using calculated densities of states of different Fermi surface sheets.