Searching for topological density wave insulators in multi-orbital square lattice systems

TL;DR

This paper investigates topological properties of density wave states in multi-orbital square lattice systems, identifying conditions for topological density wave insulators with potential experimental relevance.

Contribution

It introduces a framework for realizing topological density wave insulators in multi-orbital systems by symmetry considerations and effective potentials.

Findings

Nodal density wave states with Dirac points can be protected by lattice symmetries.

Adding an opposite symmetry order parameter can fully gap the system, creating insulators.

Topological density wave insulators can be achieved via staggered on-site potentials.

Abstract

We study topological properties of density wave states with broken translational symmetry in two-dimensional multi-orbital systems with a particular focus on t$_{2g}$ orbitals in square lattice. Due to distinct symmetry properties of d-orbitals, a nodal charge or spin density wave state with Dirac points protected by lattice symmetries can be achieved. When an additional order parameter with opposite reflection symmetry is introduced to a nodal density wave state, the system can be fully gapped leading to a band insulator. Among those, topological density wave (TDW) insulators can be realized, when an effective staggered on-site potential generates a gap to a pair of Dirac points connected by the inversion symmetry which have the same topological winding numbers. We also present a mean-field phase diagram for various density wave states, and discuss experimental implications of our results.