Low-temperature quantum relaxation of single two-dimensional vortices in an epitaxial Tl2Ba2Ca2Cu3Ox thin film

Time-logarithmic magnetic-relaxation measurements have been obtained in an epitaxial Tl2Ba2Ca2Cu3Ox thin film for the zero-field cooled and remanent magnetization, with low and moderate applied magnetic fields. With low fields (Ha=50 Oe), the normalized magnetic relaxation rates, Sd(M/Mi)/d lnt, are temperature independent below T3.4 K, and the transition from the thermal to the quantum regime appears to be quite sharp. With moderate fields (Ha=500 Oe), the transition becomes smooth and takes place at temperatures higher than with low fields, T7 K. This seems to indicate that the mechanism responsible for low-temperature relaxation would be nondissipative Hall tunneling of two-dimensional vortices, rather than dissipative vortex motion.