Anisotropic superconductivity in bulk CaC6

The intercalated graphite superconductor CaC6 with T-c similar to 11.5 K has been characterized with angular dependent magnetoresistance measurements. Above T-c, the interplane resistivity can be fitted to the Bloch-Gruneisen model providing a Debye temperature of theta(D)=175 K. From these parameters, the McMillan formula yields an electron-phonon coupling constant lambda similar to 1.1, placing this material in the intermediate-to-strong coupling regime. For 1.4 K < T < T-c, the upper critical field B-c2 is found to be anisotropic and linear in temperature.