Dynamic regimes in YBCO in applied magnetic field probed by swept frequency microwavemeasurements

Abstract

We report measurements of the microwave resistivity inYBa2Cu3O7−δ (YBCO), in the presence of an applied magnetic field. Measurements are performed as afunction of frequency, over a continuum spectrum between 6 and 20 GHz, by means of aCorbino disc geometry. These data allow for a direct identification of differentdynamical regimes in the dissipation of YBCO in the presence of an applied magneticfield. While at high temperatures a frequency independent resistivity is observed,at lower temperatures we find a marked frequency dependence. The line in the(H,T) plane at which this change in the dynamical regime is observed is clearly identified anddiscussed in terms of vortex motion and fluctuational resistivity.