Interplay of frustration, magnetism, charge ordering, and covalency in a model of Na0.5CoO2

TL;DR

This paper models Na0.5CoO2 to understand how frustration, magnetism, charge order, and covalency interact, revealing an insulating phase consistent with experimental observations and highlighting the complex interplay of these factors.

Contribution

It introduces a comprehensive Hamiltonian model that captures the subtle interplay of charge, magnetic, and covalent effects in Na0.5CoO2, explaining experimental phenomena.

Findings

Predicts an insulating phase similar to a covalent insulator

Explains small charge gap and charge ordering

Accounts for large magnetic moment and optical conductivity

Abstract

We investigate an effective Hamiltonian for Na0.5CoO2 that includes the electrostatic potential due to the ordered Na ions and strong electronic correlations. This model displays a subtle interplay between metallic and insulating phases and between charge and magnetic order. For realistic parameters, the model predicts an insulating phase with similarities to a covalent insulator. We show that this interpretation gives a consistent explanation of experiments on Na0.5CoO2, including the small degree of charge ordering, the small charge gap, the large moment, and the optical conductivity.