Cooperative Effect of Coulomb Interaction and Electron-Phonon Coupling on the Heavy Fermion State in the Two-Orbital Periodic Anderson Model

TL;DR

This study reveals that in a two-orbital periodic Anderson model, Coulomb interaction and electron-phonon coupling cooperatively enhance the heavy fermion state, contrasting with single-orbital models where they compete, with implications for orbital and lattice fluctuations.

Contribution

It demonstrates the cooperative enhancement of the heavy fermion state by Coulomb interaction and electron-phonon coupling in a two-orbital model, using dynamical mean-field theory.

Findings

Heavy fermion state is significantly enhanced by both Coulomb interaction and electron-phonon coupling.

Orbital and lattice fluctuations are increased, while charge and spin fluctuations are suppressed.

Distinct phonon softening modes are observed depending on the interaction strength.

Abstract

We investigate the two-orbital periodic Anderson model, where the local orbital fluctuations of f-electrons couple with a two-fold degenerate Jahn-Teller phonon, by using the dynamical mean-field theory. It is found that the heavy fermion state caused by the Coulomb interaction between f-electrons U is largely enhanced due to the electron-phonon coupling g, in contrast to the case with the single-orbital periodic Anderson model where the effects of U and g compete to each other. In the heavy fermion state for large $U$ and g, both the orbital and lattice fluctuations are enhanced, while the charge (valence) and spin fluctuations are suppressed. In the strong coupling regime, a sharp soft phonon mode with a large spectral weight is observed for small U, while a broad soft phonon mode with a small spectral weight is observed for large U. The cooperative effect of U and g for half-filling with two f-electrons per atom $n_f=2$ is more pronounced than that for quarter-filling with $n_f=1$.