Electromagnon dispersion probed by inelastic x-ray scattering

TL;DR

This paper demonstrates the use of inelastic x-ray scattering to detect electromagnon excitations and magnon-phonon coupling in LiCrO₂, revealing magnetic correlations and novel excitations in different magnetic phases.

Contribution

It introduces a method to measure magnetic correlations via IXS by exploiting strong magnon-phonon coupling in LiCrO₂, expanding the capabilities of IXS beyond phonons.

Findings

Detection of electromagnons and two-magnon excitations in LiCrO₂

Observation of electromagnons in both magnetically ordered and paramagnetic phases

Prediction of similar strong coupling in other frustrated magnets

Abstract

Inelastic x-ray scattering with meV energy resolution (IXS) is an ideal tool to measure collective excitations in solids and liquids. In non-resonant scattering condition, the cross section is strongly dominated by lattice vibrations (phonons). However, it is possible to probe additional degrees of freedom such as magnetic fluctuations that are strongly coupled to the phonons. The IXS spectrum of the coupled system will contain not only the phonon dispersion (majority component) but also the so far undetected magnetic correlation function (minority component). Here we report the discovery of strong magnon-phonon coupling in LiCrO$_2$ that enables the measurement of magnetic correlations throughout the Brillouin-zone via IXS. We found electromagnon excitations and electric dipole active two-magnon excitations in the magnetically ordered phase and paraelectromagnons in the paramagnetic phase of LiCrO$_2$. We predict that the numerous group of (frustrated) magnets with dominant direct exchange and non-collinear magnetism shows similarly strong coupling and surprisingly large and measurable IXS cross section for magnons and multi-magnon processes.