Local moment formation in the superconducting state of a doped Mott insulator.

A microscopic theory is presented for the local moment formation near a nonmagnetic impurity or a copper defect in high-Tc superconductors. We use a renormalized mean-field theory of the t-J model for a doped Mott insulator and study the fully self-consistent, spatially unrestricted solutions of the d-wave superconducting (SC) state in both the spin S=0 and S=1/2 sectors. We find a transition from the singlet d-wave SC state to a spin doublet SC state when the renormalized exchange coupling exceeds a doping dependent critical value. The induced S=1/2 moment is staggered and localized around the impurity. It arises from the binding of an S=1/2 nodal quasiparticle to the impurity. The local density of states is calculated and connections to NMR and STM experiments are discussed.