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

摘要

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