Anisotropic superconductivity in bulk Ca C6

The intercalated graphite superconductor Ca C6 with Tc ∼11.5 K has been characterized with angular dependent magnetoresistance measurements. Above Tc, the interplane resistivity can be fitted to the Bloch-Grüneisen model providing a Debye temperature of θD =175 K. From these parameters, the McMillan formula yields an electron-phonon coupling constant λ∼1.1, placing this material in the intermediate-to-strong coupling regime. For 1.4 K<T< Tc, the upper critical field Bc2 is found to be anisotropic and linear in temperature.