Competition between Hund-Rule Coupling and Kondo Effect

TL;DR

This paper explores how Hund-rule coupling influences the Kondo effect, revealing that it reduces the Kondo temperature and alters low-energy interactions, with implications for impurity spin dynamics.

Contribution

It demonstrates that Hund-rule coupling acts as an irrelevant perturbation but significantly impacts the Kondo temperature and low-energy physics in the extended Kondo model.

Findings

Hund-rule coupling decreases the Kondo temperature $T_K$.

The Hund-rule coupling becomes an irrelevant perturbation at the strong coupling fixed point.

It induces a ferromagnetic exchange interaction between the impurity spin and Kondo resonance states.

Abstract

We investigate a problem about the competition between the hybridization and the Hund-rule coupling by applying the Wilson numerical renormalization-group method to the extended Kondo model where the impurity spin interacts via the Hund-rule coupling, with an extra spin which is isolated from the conduction electrons. It is shown that the Hund-rule coupling is an irrelevant perturbation against the strong coupling fixed point. However, the Hund-rule coupling decreases the characteristic energy $T_K$ drastically to the lower side and the irrelevant operator, which describes the low energy physics, takes a form of ferromagnetic exchange interaction between the extra spin and the Kondo resonance states because of the existence of the Hund-rule coupling.