Kondo effect of impurity moments in d-wave superconductors: Quantum phase transition and spectral properties

Abstract

We discuss the dynamics of magnetic moments in d-wave superconductors, in particular we focus on moments induced by doping non-magnetic impurities into cuprates. The interaction of such moments with the Bogoliubov quasiparticles of the superconductors can be decribed by variants of the pseudogap Kondo model, characterized by a power-law density of states at the Fermi level. The Numerical Renormalization Group technique is employed to investigate this Kondo problem for realistic band structures and particle-hole asymmetries, both at zero and finite temperatures. In particular, we study the boundary quantum phase transition between the local-moment and the asymmetric strong-coupling phases, and argue that this transition has been observed in recent nuclear magnetic resonance experiments. We determine the spectral properties of both phases, the location of the critical point as function of Kondo coupling and doping, and discuss the quantum-critical cross-overs near this phase transition. In addition, the changes in the local density of states around the impurity are calculated as function of temperature, being relevant to scanning tunneling microscopy experiments.