Realization of Strong Coupling Fixed Point in Multilevel Kondo Models

TL;DR

This paper investigates multilevel Kondo models with four and six stable points, revealing orbital Kondo effects at low temperatures that explain enhanced electronic properties in certain filled-skutterudite materials.

Contribution

It demonstrates the realization of strong coupling fixed points in multilevel Kondo models, extending the understanding of orbital Kondo effects beyond two-level systems.

Findings

Orbital Kondo effects occur at low temperatures in multilevel models.

The results explain enhanced Sommerfeld coefficients in specific materials.

Numerical and perturbative methods confirm the fixed point realization.

Abstract

Impurity four- and six-level Kondo model, in which an ion is tunneling among four- and six-stable points and interacting with surrounding conduction electrons, are investigated by using the perturbative and numerical renormalization group methods. It is shown that purely orbital Kondo effects occur at low temperatures in these systems which are direct generalizations of the Kondo effect in the so-called two-level system. This result offers a good explanation for the enhanced and magnetically robust Sommerfeld coefficient observed in SmOs_4Sb_12 and some other filled-skutterudites.