Local Heavy Quasiparticle in Four-Level Kondo Model

TL;DR

This paper investigates a four-level Kondo model where an ion tunnels among four stable points, revealing a moderately enhanced quasiparticle effective mass that explains experimental observations in certain filled-skutterudites and clathrates.

Contribution

It introduces a four-level Kondo model with tunneling ions and demonstrates how conduction electron interactions produce a moderately enhanced quasiparticle mass.

Findings

Ground state wavefunction includes excited ion states.

Effective quasiparticle mass is moderately enhanced.

Explains enhanced Sommerfeld coefficient in specific materials.

Abstract

An impurity four-level Kondo model, in which an ion is tunneling among 4-stable points and interacting with surrounding conduction electrons, is investigated using both perturbative and numerical renormalization group methods. The results of numerical renormalization group studies show that it is possible to construct the ground state wavefunction including the excited ion states if we take into account the interaction between the conduction electrons and the ion. The resultant effective mass of quasiparticles is moderately enhanced. This result offers a good explanation for the enhanced and magnetically robust Sommerfeld coefficient observed in SmOs$_4$Sb$_{12}$, some other filled-skutterudites, and clathrate compounds.