Magnetic-field switching of exciton-magnon coupling in LiNiPO$_4$

TL;DR

This study demonstrates magnetic-field control of exciton-magnon coupling in LiNiPO$_4$, revealing sharp switching behavior across different magnetic phases using pulsed fields up to 50 T.

Contribution

It shows how external magnetic fields can selectively switch exciton-magnon coupling in an antiferromagnet, advancing control over coupled magnetic and optical excitations.

Findings

Magnon sideband intensity sharply switches across magnetic phases.

Strong suppression of coupling in plateau phases.

Enhancement of coupling in canted spin states.

Abstract

Exciton-magnon transitions provide a fundamental optical fingerprint of coupled excitonic and magnetic excitations in antiferromagnets. However, controlling such coupled excitations by external fields remains a key challenge. Here we report the temperature and magnetic-field evolution of exciton-magnon coupling in the magnetoelectric antiferromagnet LiNiPO$_4$ using pulsed magnetic fields up to 50 T. The magnon sideband intensity exhibits sharp switching across field-induced magnetic phases, with strong suppression in plateau phases and enhancement in canted spin states. This behavior is attributed to the interplay between the thermal magnon population and the spin-dependent optical transition matrix element. These results demonstrate that magnetic-field control of spin degrees of freedom enables selective switching of exciton-magnon coupling in antiferromagnets.