Effect of Rattling Phonons on Sommerfeld Constant

TL;DR

This paper investigates how rattling phonons influence the electronic specific heat in a model with anharmonic phonons, revealing enhanced phonon-mediated attraction and complex electron-phonon states.

Contribution

It introduces a numerical renormalization group analysis of the Anderson model coupled with anharmonic phonons, highlighting the effects of cage potential shape on electron-phonon interactions.

Findings

Phonon-mediated attraction is enhanced in rattling-type potentials.

Deformation of the potential leads to cancellation between Coulomb repulsion and phonon attraction.

Large, magnetically robust Sommerfeld constant observed in certain conditions.

Abstract

By employing a numerical renormalization group technique, we evaluate electronic specific heat coefficient $\gamma$ of the Anderson model coupled with local anharmonic phonons for the oscillation of a caged atom. For the rattling-type cage potential with a flat and wide region in the bottom, we find that phonon-mediated attraction is largely enhanced. When the potential shape is deformed from the rattling type, there occurs a cancellation between Coulomb repulsion and the phonon-mediated attraction. In such a situation, spin and charge fluctuations are comparable to each other, leading to the realization of exotic electron-phonon complex state with large and magnetically robust $\gamma$.