Relaxation effects in HT_c-Superconducting Thin Films

Abstract
Mechanical relaxation experiments have been widely applied to bulk high temperature (HT_c) superconducting materials. In contrast to that only few results obtained on HT_c superconducting thin films were reported. None dealt with stress driven phenomena due to the high background damping from the substrate materials used. In applied magnetic fields, however, a host reed technique can be used and the measured damping then gives information about the superconducting properties of the sample. We will discuss some experimental aspects and describe the basic information which was obtained on YBa₂Cu₃O_7-x and Bi₂Sr₂CaCu₂O_8+x thin films. This includes the lower critical field, the Labusch parameter, pinning energies related to the mode1 of thermally assisted flux flow (TAFF), and a matching effect of the flux line lattice (FLL) to the thickness of the films.