Magnetic impurity coupled to interacting conduction electrons

TL;DR

This paper investigates how weak electron correlations in conduction electrons influence the Kondo temperature, revealing that Hubbard interactions both suppress and enhance T_K through different mechanisms, leading to an overall increase.

Contribution

It introduces a novel analysis of how Hubbard interactions affect the Kondo effect, showing renormalization of the Kondo coupling beyond standard models.

Findings

Hubbard interactions shift the impurity level, reducing charge fluctuations and T_K.

Spin fluctuations are enhanced, increasing the bare Kondo exchange coupling.

Overall, the Kondo temperature T_K increases due to combined effects.

Abstract

We consider a magnetic impurity which interacts by hybridization with a system of weakly correlated electrons and determine the energy of the ground state by means of an 1/N_f expansion. The correlations among the conduction electrons are described by a Hubbard Hamiltonian and are treated to lowest order in the interaction strength. We find that their effect on the Kondo temperature, T_K, in the Kondo limit is twofold: First, the position of the impurity level is shifted due to the reduction of charge fluctuations, which reduces T_K. Secondly, the bare Kondo exchange coupling is enhanced as spin fluctuations are enlarged. In total, T_K increases. Both corrections require intermediate states beyond the standard Varma-Yafet ansatz. This shows that the Hubbard interaction does not just provide quasiparticles, which hybridize with the impurity, but also renormalizes the Kondo coupling.