Polaron and bipolaron tendencies in a semiclassical model for hole-doped bismuthates

TL;DR

This study uses classical Monte Carlo simulations on a semiclassical model to explore polaron and bipolaron behaviors in hole-doped bismuthates, shedding light on their complex phase diagram and the role of electron-phonon interactions.

Contribution

It introduces a semiclassical three-orbital model with off-diagonal electron-phonon interactions and demonstrates persistent polaron correlations at high temperatures and doping levels.

Findings

Polaron and bipolaron correlations persist at high temperatures.

Heating and doping induce similar melting of bond-disproportionated insulators.

Polaron physics may unify understanding of bismuth perovskite phases.

Abstract

Bismuth perovskites ABiO$_3$ (A = Sr, Ba) host a variety of peculiar phenomena including bond-disproportionated insulating phases and high-temperature superconductivity upon hole doping. While the mechanisms underlying these phenomena are still debated, off-diagonal electron-phonon ($e$-ph) coupling originating from the modulation of the orbital overlaps has emerged as a promising candidate. Here, we employ classical Monte Carlo simulations to study a semiclassical three-orbital model with off-diagonal $e$-ph interactions. We demonstrate the existence of a (bi)polaron correlations that persists in the model at high temperatures and for hole doping away from the bond-disproportionated insulating phase. Using a spatiotemporal regression analysis between various local quantities and the lattice degrees of freedom, we also identify the similarity between heating- and doping-induced melting of a bond-disproportionated insulator at a microscopic level. Our results imply that (bi)polaron physics can be a unifying concept that helps us understand the rich bismuth perovskite phase diagram.