Linear and nonlinear electrodynamic response of bulk CaC6 in the microwave regime

The linear and nonlinear response to a microwave electromagnetic field of two c-axis oriented polycrystalline samples of the newly discovered superconductor CaC6 (Tc = 11.5 K) is studied in the superconducting state down to 2 K. The surface resistance Rs and the third order intermodulation distortion, arising from a two-tone excitation, have been measured as a function of temperature and microwave circulating power. Experiments are carried out using a dielectrically loaded copper cavity operating at 7 GHz in a "hot finger" configuration. The results confirm recent experimental findings that CaC6 behaves as a weakly-coupled, fully gapped, superconductor. The weak power dependence of Rs encourages a further investigation of this novel superconductor as a possible alternative to Nb in specific microwave applications.