Kondo Effect in Unconventional Superconductors

Abstract

A new type of Kondo effect in unconventional superconductors is studied theoretically by using the Wilson's numerical renormalization group method. In this case, orbital degrees of freedom of a Cooper pair play an important role. It produces multichannel exchange couplings with a magnetic impurity, although the impurity is just a local spin. Here we focus on a p x +i p y -wave state which is a fully gapped system. In this case, the ground state is always a spin doublet in all the T K /Δ region, and the local spin is shrunk by the Kondo effect in the strong coupling region ( T K /Δ→∞). Here T K and Δ are the Kondo temperature and the superconducting energy gap, respectively. It indicates that the spin of the ground state is generated by the orbital effect of the Cooper pairs. This is completely different from the s -wave pairing case where a Kondo singlet is stabilized for large T K /Δ values. This type of Kondo effect reflects the symmetry of the conduction electron system.