Site-selective nuclear magnetic relaxation time in a superconducting vortex state

On the basis of the microscopic Bogoliubov-de Gennes theory, the dependence of the nuclear spin relaxation time T₁ around vortices on the temperature and field is studied comparatively for both s-wave superconductor and d-wave superconductor. Reflecting low energy electronic excitations associated with the vortex core, the dependence of T₁ on the site and temperature deviate from those of the zero-field case, and T₁ becomes faster with approaching the vortex core. In the core region, T^-1₁ has a new peak below the superconducting transition temperature T_c. The dependence of the overall T₁(T) on the field for s-wave and d-wave superconductors is investigated and analyzed in terms of the local density of states. The NMR study by the dependence of T₁ on the resonance field may be a new method to probe the spatial resolved vortex core structure in various conventional and unconventional superconductors.