Experimental study of the inductance of pinned vortices in superconductingYBa3Cu3O7-delta films

Using a two-coil mutual inductance method, we have measured the complex res istivity rho (v)(T,B-c) of pinned vortices in c-axis pulsed laser deposited YBa2Cu3O7-delta films with magnetic fields applied perpendicular to the fi lm. At low frequencies (<100 kHz) <rho>(v) is inductive and is inversely pr oportional to the Labusch parameter, the average vortex pinning force const ant kappa (exp). The observed weakening of kappa (exp) with increasing vort ex density and temperature is consistent with a simple model based on exten ded pinning defects. We conclude that the effective radius of the defects i s about 3-8 Angstrom, and that, thermal supercurrent (phase) fluctuations h ave their full classical amplitude down to 5 K in the bandwidth set by the characteristic depinning frequency.