Theory of NMR as a local probe for the electronic structure in the mixed state of the high-T-c cuprates

We argue that nuclear-magnetic-resonance experiments are a site-sensitive p robe for the electronic spectrum in the mixed state of the high-T-c cuprate s. Within a spin-fermion model, we show that the Doppler-shifted electronic spectrum arising from the circulating supercurrent changes the low-frequen cy behavior of the imaginary part of the spin susceptibility. For a hexagon al vortex lattice, we predict that these changes lead to (i) a unique depen dence of the Cu-63 Spin lattice relaxation rate, 1/T-1, on resonance freque ncy, and (ii) a temperature dependence of T-1 which varies with frequency. We propose a nuclear quadrupole experiment to study the effects of a unifor m supercurrent on the electronic structure and predict that T-1 varies with the direction of the supercurrent.