Light-matter interaction in antiferromagnets: the exchange-induced magnetic dipole mechanism

TL;DR

This paper introduces a new exchange-induced magnetic dipole mechanism explaining exciton-magnon absorption in antiferromagnets, aligning well with experimental observations in KCuF3.

Contribution

It presents a novel theoretical mechanism for exchange-induced exciton-magnon absorption involving magnetic dipole transitions and validates it with experimental data.

Findings

Selection rules match observed exciton-magnon transitions.

Magnon density of states explains optical magnon sidebands.

Mechanism applies to quasi one-dimensional antiferromagnets.

Abstract

We propose a novel mechanism for exchange-induced exciton-magnon absorptions via hopping between two antiferromagnetically coupled sites and a simultaneous magnetic dipole transition to an excited orbital state. The obtained selection rules correspond to ones for magnetic dipole transitions and are in agreement with the exciton-magnon transitions observed in the quasi one-dimensional Heisenberg antiferromagnet KCuF3. The calculated magnon density of states in combination with a structure dependent factor identifies the observed optical magnon sideband to originate from transverse magnon modes.