Microwave properties of RE-Ni2B2C (RE = Y, Er) superconducting thin films

A comparative study of the microwave properties of YNi2B2C and ErNi2B2C superconducting films is reported. The measurements were performed using a microstrip resonator (f = 2 GHz) and a microwave cavity (f = 87 GHz). The analysis of the temperature dependence of the surface impedance Z(s) confirms that YNi2B2C compound is a conventional BCS (s-wave) superconductor On the contrary, ErNi2B2C samples show an anomalous behaviour in both the surface resistance and penetration depth. This is tentatively ascribed to pair breaking effects on the superconducting density of states. A simplified generalisation of the Abrikosov-Gorkov theory, proposed by Machida, is successfully applied to describe the penetration depth data in the antiferromagnetic compound, while for the surface resistance granular effects cannot be ruled out.