Possible proximity of the Mott insulating Iridate Na2IrO3 to a topological phase: Phase diagram of the Heisenberg-Kitaev model in a magnetic field

TL;DR

This paper explores the phase diagram of the Heisenberg-Kitaev model in a magnetic field for Na2IrO3, revealing potential topological phases and multicritical points driven by strong spin-orbit coupling.

Contribution

It provides the first detailed analysis of the phase diagram of the Heisenberg-Kitaev model under magnetic fields, highlighting the possibility of topological phases in Na2IrO3.

Findings

Identification of a topologically ordered phase in the model

Discovery of multicritical points between ordered phases

Rich phase diagram with symmetry-breaking magnetic phases

Abstract

Motivated by the recent experimental observation of a Mott insulating state for the layered Iridate Na2IrO3, we discuss possible ordering states of the effective Iridium moments in the presence of strong spin-orbit coupling and a magnetic field. For a field pointing in the [111] direction - perpendicular to the hexagonal lattice formed by the Iridium moments - we find that a combination of Heisenberg and Kitaev exchange interactions gives rise to a rich phase diagram with both symmetry breaking magnetically ordered phases as well as a topologically ordered phase that is stable over a small range of coupling parameters. Our numerical simulations further indicate two exotic multicritical points at the boundaries between these ordered phases.