Correlation-Driven Charge Order at a Mott Insulator - Band Insulator Digital Interface

TL;DR

This study uses correlated band theory to explore charge order phenomena at LaTiO3/SrTiO3 interfaces, revealing robust charge disproportionation and orbital ordering influenced by electron correlations and lattice effects.

Contribution

It demonstrates that charge ordering and orbital phenomena at the interface are driven by electron correlations, with lattice relaxation affecting conduction but not the core charge order.

Findings

Charge disproportionation occurs at the interface.

Orbital ordering is stabilized in the Ti3+ ions.

Lattice relaxation shifts the Hubbard band but preserves charge order.

Abstract

To study digital Mott insulator LaTiO3 and band insulator SrTiO3 interfaces, we apply correlated band theory (LDA+U) to (n,m) multilayers, 1<n,m<9. If the on-site repulsion on Ti is large enough to model the magnetic insulating behavior of cubic bulk LaTiO3, the charge imbalance at the interface is found in all cases to be accommodated by disproportionation (Ti4+ + Ti3+), charge ordering, and Ti3+ d_xy-orbital ordering, with antiferromagnetic exchange coupling between the spins in the interface layer. Lattice relaxation affects the conduction behavior by shifting (slightly but importantly) the lower Hubbard band, but the disproportionation and orbital ordering are robust against relaxation.