Kitaev-Heisenberg Model on Honeycomb Lattice: Possible Exotic Phases in Iridium Oxides $A_2$IrO$_3$

TL;DR

This paper investigates a spin-1/2 Hamiltonian on a honeycomb lattice relevant to iridates, revealing a rich phase diagram including spin-liquid, Ne9el, and stripy antiferromagnetic phases through exact diagonalization and spin-wave analysis.

Contribution

It introduces a model interpolating between Heisenberg and Kitaev interactions, uncovering novel phases and phase transitions in iridate materials.

Findings

Identification of an extended spin-liquid phase near the Kitaev limit.

Discovery of a conventional Ne9el state close to the Heisenberg limit.

Existence of a stripy antiferromagnetic phase separating the two main phases.

Abstract

We derive and study a spin one-half Hamiltonian on a honeycomb lattice describing the exchange interactions between Ir$^{4+}$ ions in a family of layered iridates $A_2$IrO$_3$ ($A$=Li,Na). Depending on the microscopic parameters, the Hamiltonian interpolates between the Heisenberg and exactly solvable Kitaev models. Exact diagonalization and a complementary spin-wave analysis reveal the presence of an extended spin-liquid phase near the Kitaev limit and a conventional N\'eel state close to the Heisenberg limit. The two phases are separated by an unusual stripy antiferromagnetic state, which is the exact ground state of the model at the midpoint between two limits.