Detecting flux creep in superconducting YBCO thin films via damping of the oscillations of a levitating permanent magnet

Abstract

The damping of the oscillations of a small permanent magnet (spherical shape, radius 0.1 mm) levitating between two parallel epitaxial YBCO films is measured as a function of oscillation amplitude and temperature. At small amplitudes the dissipation is found to be orders of magnitude lower than in bulk YBCO, Q-factors exceeding one million at low temperatures. With increasing amplitude the dissipation becomes exponentially large, exceeding the bulk values at large drives. We describe our results by calculating the ac shielding currents flowing through trapped flux whose motion gives rise to electric fields. We find dissipation to originate from different mechanisms of flux dynamics.