Study of the vortex dynamics as a function of frequency in the microwave range

Abstract

The frequency dependence of the transport properties provides noticeable informations on the vortex matter in superconductors. In particular, low (<100 MHz) and high (of order 10 GHz) frequency response give different informations on the vortex dynamics: while at low frequency large distance motion of vortices is predominant, at higher frequencies vortices tend to oscillate around their equilibrium positions. Few reports have been presented in the past related to the study of the intermediate frequency regime, and to the evolution of one regime into the other. We present here an experimental study as a function of frequency, in the range 1–20 GHz, over a continuous frequency spectrum (Corbino disc technique), in presence of an applied magnetic field. Data are presented for both YBa 2Cu 3O 7− δ and MgB 2 superconductors. We also discuss the data as a function of frequency and show to what extent existing theories are able to fit the measured data.