Orbital order in Mott insulators of spinless p-band fermions

TL;DR

This paper investigates the orbital order phenomena in Mott insulators formed by spinless p-band fermions in 2D optical lattices, revealing new models and ordering mechanisms influenced by lattice geometry.

Contribution

It introduces effective orbital exchange models for different lattice geometries and analyzes orbital ordering and fluctuation effects in these systems.

Findings

Orbital exchange in square lattices maps to a pseudospin-1/2 XXZ model.

Geometric frustration leads to a quantum 120 degree model on triangular, honeycomb, and Kagome lattices.

Orbital wave fluctuations select ground states via order by disorder on the honeycomb lattice.

Abstract

A gas of strongly interacting spinless p-orbital fermionic atoms in 2D optical lattices is proposed and studied. Several interesting new features are found. In the Mott limit on a square lattice, the gas is found to be described effectively by an orbital exchange Hamiltonian equivalent to a pseudospin-1/2 XXZ model. For a triangular, honeycomb, or Kagome lattice, the orbital exchange is geometrically frustrated and described by a new quantum 120 degree model. We determine the orbital ordering on the Kagome lattice, and show how orbital wave fluctuations select ground states via the order by disorder mechanism for the honeycomb lattice. We discuss experimental signatures of various orbital ordering.