THERMALLY ACTIVATED VORTEX MOTION IN YBA2CU3O7, WIRE NETWORKS

With a mutual inductance method we have measured the temperature depen dence of the complex AC impedance Z = R + i omega L of high quality YB a2Cu3O7 wire networks. In a perpendicular magnetic field the real and the imaginary part of Z exhibit oscillations resulting from flux quant ization in the loops of the network. The relative amplitude of the osc illations of the inverse effective sheet inductance L(-1) is consisten t with a model where L(-1) is renormalized by thermally activated vort ex motion.