Charge ordering and magnetism in quarter-filled Hubbard-Holstein model

TL;DR

This paper investigates the charge ordering and magnetic phases in a two-dimensional quarter-filled Hubbard-Holstein model, revealing a charge-ordered antiferromagnetic phase relevant to LaAlO3-SrTiO3 interfaces.

Contribution

It introduces a detailed phase diagram for the quarter-filled Hubbard-Holstein model and identifies a charge-ordered antiferromagnetic phase consistent with experimental observations.

Findings

Identification of a charge-ordered antiferromagnetic phase at quarter-filling

Relevance of the model to LaAlO3-SrTiO3 interface properties

Phase diagrams showing various electronic and magnetic states

Abstract

We study a two-dimensional Hubbard-Holstein model with phonons treated in the adiabatic limit. A Hartree-Fock decomposition is employed for the Hubbard term. A range of electronic densities are discussed with special emphasis on the quarter-filling ($n=0.5$). We argue that the quarter-filled system is relevant for the electronic properties observed at the interface between LaAlO$_3$ and SrTiO$_3$, where half-electron per unit cell is transferred to the TiO$_2$ layer as a consequence of the polar discontinuity at the interface. In addition to presenting the overall phase diagrams, we identify an interesting charge-ordered antiferromagnetic phase for $n=0.5$, which was also reported recently in the ab-initio study of the LaAlO$_3$-SrTiO$_3$ interface.