Abstract:
|
Time-logarithmic magnetic-relaxation measurements have been obtained in an epitaxial
Tl
2
Ba
2
Ca
2
Cu
3
O
x
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 rates, S≡‖d(M/
M
i
)/d lnt‖, are temperature independent below T≃3.4 K, and the transition from the thermal to the quantum regime 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≃7 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. |