Phase transitions in the Hubbard model for the bismuth nickelate

TL;DR

This paper investigates phase transitions in the Hubbard model for bismuth nickelate, revealing how charge, magnetic, and orbital orders emerge and persist at low temperatures, with insights into metal-insulator crossover.

Contribution

It combines dynamical mean-field theory with quantum Monte Carlo to analyze the effects of orbital degeneracy and attractive interactions in the Hubbard model for bismuth nickelate.

Findings

Charge and magnetic orders are stable against thermal fluctuations.

Orbital degeneracy stabilizes ferromagnetic and orbital ordered states.

Crossover between metallic and insulating states is characterized.

Abstract

We study low temperature properties of the Hubbard model for the bismuth nickelate, where degenerate orbitals in the nickel ions and a single orbital in the bismuth ions are taken into account, combining dynamical mean-field theory with the continuous-time quantum Monte Carlo method. We discuss the effect of the attractive interactions to mimic the valence skipping phenomenon in the bismuth ions. We demonstrate how the charge and magnetically ordered states are stable against thermal fluctuations. It is furthermore clarified that the ferromagnetically ordered and orbital ordered states are stabilized due to the presence of the orbital degeneracy at low temperatures. The crossover between metallic and insulating states is also discussed.