ZEITSCHRIFT FÜR PHYSIK B CONDENSED MATTER 101, 561 (1996)

M. Wurlitzer, F. Mrowka, P. Esquinazi, K. Rogacki, B. Dabrowski, E. Zeldov, T. Tamegai, S. Ooi

Abstract

We have studied the hysteretic loss and the shielding capability of Bi₂Sr₂CaCu₂0₈and YBa₂Cu₄O₈ crystals as a function of ac field (µ₀H < 1mT), frequency, and temperature at small dc fields (µ₀H_a < 1mT) near the critical temperature T_c. We show that the global ac field dependence of the susceptibility can be described in terms of a geometrical barrier model in agreement with local permeability results. At temperatures very near T_c, however, we observe a crossover to diffusive behavior. The frequency dependence of the temperature of the dissipation maximum at finite dc fields shows a thermally activated behavior.