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

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 (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.

Automated summary

In this study, classical Monte Carlo simulations were used to investigate a semiclassical three-orbital model with off-diagonal electron-phonon interactions, demonstrating the existence of (bi)polaron correlations at high temperatures and under hole doping conditions. By analyzing the relationship between various local quantities and lattice degrees of freedom, similarities were identified between heating- and doping-induced melting of a bond-disproportionated insulator at a microscopic level. The results suggest that (bi)polaron physics can serve as a unifying concept to understand the complex phase diagram of bismuth perovskites.