Exciton-spin interactions in antiferromagnetic charge-transfer insulators

TL;DR

This paper derives a microscopic model for exciton-spin interactions in charge-transfer insulators, revealing how excitons influence magnetic properties and optical spectra in these correlated materials.

Contribution

It introduces a minimal coupled-cluster model capturing exciton-spin couplings and magnetic anisotropy in charge-transfer insulators, advancing understanding of their optical and magnetic behavior.

Findings

Strong magnetic exchange couplings with spatial anisotropy

Optical excitation spectrum shows magnetic sidebands

Spin-flip excitations explain magnetic sidebands observed experimentally

Abstract

We derive exciton-spin interactions from a microscopic correlated model that captures important aspects of the physics of charge-transfer (CT) insulators to address magnetism associated with exciton creation. We present a minimal model consisting of coupled clusters of transition metal d and ligand p orbitals that captures the essential features of the local atomic and electronic structure. First, we identify the lowest-energy state and optically allowed excited states within a cluster by applying the molecular orbital picture to the ligand p orbitals. Then, we derive the effective interactions between two clusters mediated by intercluster hoppings, which include exciton-spin couplings. The interplay of the correlations and the spatial structure of the CT exciton leads to strong magnetic exchange couplings with spatial anisotropy. Finally, we calculate an optical excitation spectrum in our effective model to obtain insights into magnetic sidebands optically observed in magnetic materials. We demonstrate that the spin-flip excitation due to the strongly enhanced local spin interactions around the exciton gives rise to the magnetic sidebands.