Spin Hamiltonian of Hyperkagome Na4Ir3O8

TL;DR

This paper derives the spin Hamiltonian for the quantum spin liquid Na4Ir3O8, estimating exchange interactions and supporting isotropic Heisenberg models through electronic structure calculations.

Contribution

It provides a detailed derivation and estimation of the spin Hamiltonian for Na4Ir3O8, highlighting the dominance of isotropic direct exchange interactions.

Findings

Exchange interaction magnitude matches experimental estimates.

Direct exchange dominates over superexchange in the studied parametrization.

Supports isotropic Heisenberg model assumptions for this quantum spin liquid.

Abstract

We derive the spin Hamiltonian for the quantum spin liquid Na4Ir3O8, and then estimate the direct and superexchange contributions between near neighbor iridium ions using a tight binding parametrization of the electronic structure. We find a magnitude of the exchange interaction comparable to experiment for a reasonable value of the on-site Coulomb repulsion. For one of the two tight binding parametrizations we have studied, the direct exchange term, which is isotropic, dominates the total exchange. This provides support for those theories proposed to describe this novel quantum spin liquid that assume an isotropic Heisenberg model.