MICROWAVE RESPONSE OF ANISOTROPIC HIGH-TEMPERATURE-SUPERCONDUCTOR CRYSTALS

Microwave penetration and losses are derived for the anisotropic norma l and superconducting states of single crystals in the shape of thin p latelets oriented parallel and perpendicular to the oscillating electr omagnetic field. For platelet crystals with the microwave field parall el to the major flat faces, the large anisotropy in the -normal state can result in dissipation dominated by microwave field penetration thr ough the thin edges rather than across the main faces. The influence o f the extreme anisotropy is also considered for the superconducting st ate and can account for an anomalous peak in microwave loss below T(c) sometimes observed in Bi-Sr-Ca-Cu-O crystals. When crystals are mount ed with their flat faces perpendicular to the microwave field, the los ses in both the normal and superconducting states are shown to be stro ngly peaked towards the outer perimeter of the crystals. This makes cr itical demands on the degree of perfection of such regions, if the mic rowave measurements are not to be complicated by nonintrinsic effects associated with local imperfections.