Fluxon thermal motion detected by nuclear spin echo decay measurements:Y89NMR inYBa2Cu3O7

A new NMR approach was devised to investigate thermal motion of vortices based on the observation of dephasing effects of the transverse nuclear magnetization below ${\mathit{T}}_{\mathit{c}}$. The effect was observed in ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ spin-spin relaxation time ${\mathit{T}}_2$ measurements of ${\mathrm{TBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ for two crystal orientations with respect to the applied magnetic field. The data were fitted with a simple model of diffusion of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ 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 vortices’ motion well below ${\mathit{T}}_{\mathit{c}}$ with reasonable activation energies were derived.