Reentrant charge ordering caused by polaron formation

TL;DR

This paper investigates how polaron formation influences charge ordering transitions in a 2D Hubbard model, revealing reentrant behavior linked to temperature-dependent polaron bandwidth, explaining experimental observations in layered manganites.

Contribution

It introduces a model showing how polaron effects cause reentrant charge ordering transitions, providing a theoretical explanation for experimental phenomena in manganites.

Findings

Charge order can appear, collapse, and reappear with temperature in ferromagnetic states.

Reentrant charge ordering occurs partly due to polaron bandwidth changes.

The model explains observed reentrant behavior in LaSr$_2$Mn$_2$O$_7$.

Abstract

Based on a two-dimensional extended Hubbard model with electron-phonon interaction, we have studied the effect of polaron formation on the charge ordering (CO) transition. It is found that for fully ferromagnetically ordered spins the CO state may go through a process of appearance, collapse and reappearance with decreasing temperature. This is entirely due to a emperature-dependent polaron bandwidth. On the other hand, when a paramagnetic spin state is considered, only a simple reentrant behavior of the CO transition is found, which is only partly due to polaron effect. This model is proposed as an explanation of the observed reentrant behavior of the CO transition in the layered manganite LaSr$_2$Mn$_2$O$_7$.