Low Field Microwave Absorption of Granular Superconductors

Granular superconductors screen out an applied magnetic field only imperfectly. Fluxons enter the intergranular spaces at very low fields and their presence can be easily detected by microwave absorption. Experiments on high T>c superconductors have allowed the identification of two absorption processes, (a) viscous fluxon motion in the microwave field and (b) fluxon nucleation and annihilation by the induced microwave current. Both processes are also observed in conventional superconductors but not always with the same characteristics. © 1989 IOP Publishing Ltd.