Phase diagram of Holstein-Kondo lattice model at half-filling

TL;DR

This paper investigates the phase diagram of the Holstein-Kondo lattice model at half-filling, revealing transitions between Kondo insulator, metal, and bipolaronic insulator phases influenced by electron-phonon and Kondo interactions.

Contribution

It provides the first detailed zero-temperature phase diagram of the Holstein-Kondo lattice model using dynamical mean-field theory and exact diagonalization, highlighting the interplay of spin and charge fluctuations.

Findings

Kondo insulator state when Kondo coupling dominates

Kondo insulator-metal transition with increasing electron-phonon coupling

Transition to bipolaronic insulating phase at high electron-phonon coupling

Abstract

We study the Kondo lattice model which is modified by the Holstein term, involving both the Kondo exchange coupling and the electron-phonon coupling constants, characterized by $J$ and $g$, respectively. The model is solved by employing the dynamical mean-field theory in conjunction with exact diagonalization technique. A zero temperature phase diagram of symmetry unbroken states at half filling is mapped out which exhibits an interplay between the two interactions and accounts for both spin and charge fluctuations. When the Kondo exchange coupling is dominant the system is in Kondo insulator state. Increasing $g$ for small values of $J$ leads to a Kondo insulator-metal transition. Upon further enhancement of $g$ a transition to the bipolaronic insulating phase takes place. Also a small region with non-Fermi liquid behavior is found near the Kondo insulator-metal transition.