Role of the superexchange interaction in magnetic transition and polaron crossover

TL;DR

This paper investigates how superexchange interactions influence magnetic transitions and polaron behavior in the Hubbard-Holstein model, revealing the interplay between electron-phonon coupling, electron concentration, and magnetic interactions.

Contribution

It introduces a variational approach combining the modified Lang-Firsov and squeezing transformations to analyze magnetic and polaronic phenomena in the model.

Findings

Polaron crossover depends on electron-phonon coupling and electron concentration.

Superexchange interaction suppresses ferromagnetic transition.

Magnetic transition and polaron crossover are significantly affected by the superexchange parameter J.

Abstract

The Hubbard-Holstein model is studied including double-exchange interaction and superexchange interaction using a variational phonon basis obtained through the modified Lang-Firsov (MLF) transformation followed by the squeezing transformation. The kinetic energy, polaron crossover and magnetic transition are investigated as a function of electron-phonon ($e$-ph) coupling and electron concentration for different values of antiferromagnetic superexchange interaction ($J$) between the core spins. The polaron crossover, magnetic transition and the suppression of ferromagnetic transition with $J $ are discussed for the model.