FLUXON THERMAL MOTION DETECTED BY NUCLEAR-SPIN ECHO DECAY MEASUREMENTS - Y-89 NMR IN YBA2CU3O7

A new NMR approach was devised to investigate thermal motion of vortic es based on the observation of dephasing effects of the transverse nuc lear magnetization below T(c). The effect was observed in Y-89 spin-sp in relaxation time T2 measurements of YBa2Cu3O7 for two crystal orient ations with respect to the applied magnetic field. The data were fitte d with a simple model of diffusion of Y-89 nuclei with respect to the local magnetic field gradient generated by the moving vortices. Small values of a thermally activated effective diffusion constant of the vo rtices' motion well below T(c) with reasonable activation energies wer e derived.