THERMAL DEPINNING OF FLUX LINES IN HGBA2CUO4-199 SPIN-LATTICE RELAXATION(DELTA FROM HG)

Hg-199 NMR spin-lattice relaxation rates in an aligned powder sample o f the anisotropic high-T-c superconductor HgBa2CuO4+delta (T-c = 96 K) show anisotropy in the temperature interval 10-50 K, with an extra co ntribution present for the external magnetic field parallel to the c a xis. The extra contribution shifts with magnetic field in a way relate d to the irreversibility temperature T-irr indicating that the thermal motion of flux lines (FL's) is the cause of the extra relaxation. A s imple model is presented to analyze the relaxation data and to extract values for the correlation time tau(c) and the effective activation;e nergy U of the FL motion.