LOW-TEMPERATURE QUANTUM RELAXATION OF SINGLE 2-DIMENSIONAL VORTICES IN AN EPITAXIAL TL2BA2CA2CU3OX THIN-FILM

Time-logarithmic magnetic-relaxation measurements have been obtained i n an epitaxial Tl2Ba2Ca2Cu3Ox thin film for the zero-field cooled and remanent magnetization, with low and moderate applied magnetic fields. With low fields (H(a) = 50 Oe), the normalized magnetic relaxation ra tes, S = \d(M/M(i))/d lnt\, are temperature independent below T congru ent-to 3.4 K, and the transition from the thermal to the quantum regim e appears to be quite sharp. With moderate fields (H(a) = 500 Oe), the transition becomes smooth and takes place at temperatures higher than with low fields, T congruent-to 7 K. This seems to indicate that the mechanism responsible for low-temperature relaxation would be nondissi pative Hall tunneling of two-dimensional vortices, rather than dissipa tive vortex motion.