EFFECT OF DISSIPATION ON QUANTUM TUNNELING OF VORTICES IN TL2BA2CA2CU3O10+DELTA SUPERCONDUCTORS

The temperature and magnetic field dependence of the magnetic relaxati on rate has been investigated at low temperatures (1.8 < T < 10 K) on two Tl2Ba2Ca2Cu3O10+delta samples (epitaxial thin film and sintered pe llet). The temperature dependence gives evidence of a crossover in the mechanism of vortex motion, from classical thermal activation to quan tum tunneling as temperature decreases. The field dependence of the re laxation rate indicates a crossover in the dimensionality of vortices, from three-dimensional flux lines to two-dimensional pancake vortices as field increases. For the thin him, the temperature dependence of t he rate has been fitted to the theoretically predicted expressions for finite-temperature enhancement of the quantum rate in different regim es of dissipation. In spite of the similarity of the fits, the estimat e of the ratio of Hall to viscous drag terms in the equation of motion indicates that quantum tunneling in this system occurs in an intermed iate dissipative regime, where both terms contribute to the motion of vortices.