Anisotropic Superconductivity in the Graphite Potassium-Amalgam Intercalation Compound C₈KHg

Superconducting properties of C₈KHg have been investigated by AC magnetic susceptibility measurements. The measured values of T_c are 1.90 K and 1.70 K for two samples. From the measurements under DC magnetic field, the superconductivity is found to be the type II in all the field directions. H_c2 is markedly anisotropic, but the angular dependence of H_c2 is fairly well understood by means of the 3D anisotropic effective mass model. The characteristic parameter γ is too large, e.g. 64 or 76, to apply the 2D Josephson-coupling model. So, C₈KHg is regarded as a 3D superconductor with a very large anisotropy rather than a 2D one. As the obtained effective mass ratio is as large as 940 or 920, the electronic band structure of C₈KHg seems more anisotropic than that of C₈K. In C₄KHg, superconductivity has not been found above 1.5 K.