Local Moment Formation in the Superconducting State of a Doped Mott Insulator

TL;DR

This paper develops a microscopic theory for local moment formation near impurities in high-T_c superconductors, revealing a transition to a spin doublet state with localized moments linked to quasiparticle binding.

Contribution

It introduces a self-consistent, spatially unrestricted renormalized meanfield approach to the t-J model, showing a doping-dependent transition to a spin doublet state.

Findings

Localized S=1/2 moments form around impurities

Transition from singlet to doublet state with increasing exchange coupling

Calculated local density of states matches experimental observations

Abstract

A microscopic theory is presented for the local moment formation near a non-magnetic impurity or a copper defect in high-T_c superconductors. We use a renormalized meanfield 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 excitation to the impurity. The local density of states spectrum is calculated and connections to NMR and STM experiments are discussed.