Finite-temperature phase diagram of the Heisenberg-Kitaev model

TL;DR

This paper maps the finite-temperature phase diagram of the Heisenberg-Kitaev model on a hexagonal lattice, revealing magnetic and spin liquid phases, and compares theoretical predictions with experimental data on Na2IrO3.

Contribution

It applies a pseudofermion functional RG approach to analyze the finite-temperature phases of the Heisenberg-Kitaev model, providing new insights into exchange interactions and phase transitions.

Findings

Curie-Weiss scale changes sign, indicating a shift from antiferromagnetic to ferromagnetic exchange.

No significant frustration observed in the magnetically ordered regime.

Results align with experimental susceptibility measurements for Na2IrO3.

Abstract

We discuss the finite-temperature phase diagram of the Heisenberg-Kitaev model on the hexagonal lattice, which has been suggested to describe the spin-orbital exchange of the effective spin-1/2 momenta in the Mott insulating Iridate Na2IrO3. At zero-temperature this model exhibits magnetically ordered states well beyond the isotropic Heisenberg limit as well as an extended gapless spin liquid phase around the highly anisotropic Kitaev limit. Using a pseudofermion functional renormalization group (RG) approach, we extract both the Curie-Weiss scale and the critical ordering scale (for the magnetically ordered states) from the RG flow of the magnetic susceptibility. The Curie-Weiss scale switches sign -- indicating a transition of the dominant exchange from antiferromagnetic to ferromagnetic -- deep in the magnetically ordered regime. For the latter we find no significant frustration, i.e. a substantial suppression of the ordering scale with regard to the Curie-Weiss scale. We discuss our results in light of recent experimental susceptibility measurements for Na2IrO3.