Microwave study of high Tc granular superconductors

One of the features of granular high-T_c superconductors is the anomalous absorption of microwaves as a function of both the DC magnetic field and temperature. An attempt is made to associate the observed derivative absorption of the microwaves with the existence of micron-sized current loops formed by weak Josephson links or junctions in high-T_c granular superconductors. It is shown that microwave absorption is caused by energy dissipation in the Josephson-junction-system, which is dependent on magnetic field, microwave current, and thermal fluctuations. The implications of the absorbed microwave power in terms of heating of the irradiated sample are discussed