Ultrasonic attenuation in high-T c superconductors: a new approach to the problem of flux pinning

Abstract

Measurements of the transverse sound attenuation and velocity in ceramic YBa 2 Cu 3 O x superconductors were performed with and without a magnetic field. We observe a pronounced peak in the field-induced attenuation and an increase of the velocity at low temperatures. We attribute these effects to the transition of a rigidly pinned flux line lattice into a depinned state at higher temperatures and give a quantitative explanation in terms of thermally assisted flux flow. Depinning temperatures show a drastic dependence on the oxygen stoichiometry.