Model for twin electromagnons and magnetically induced oscillatory polarization in multiferroic RMnO$_3$

TL;DR

This paper introduces a model explaining electromagnon pairs in multiferroic R MnO3, linking their spectral features to oscillatory polarization induced by magnetostriction and spin-orbit effects, with predictions for TbMnO3.

Contribution

The model reveals the origin of electromagnon pairs and their connection to oscillatory polarization, providing new insights into multiferroic material behavior.

Findings

Electromagnon pairs are activated by magnetostriction and spin-orbit coupling.

Twin electromagnon spectral weight relates to oscillatory polarization.

TbMnO3 exhibits an oscillatory polarization 50 times larger than its uniform polarization.

Abstract

We propose a model for the pair of electromagnon excitations observed in the class of multiferroic materials {\it R}MnO$_3$ ({\it R} is a rare-earth ion). The model is based on a harmonic cycloid ground state interacting with a zone-edge magnon and its twin excitation separated in momentum space by two times the cycloid wave vector. The pair of electromagnons is activated by cross coupling between magnetostriction and spin-orbit interactions. Remarkably, the spectral weight of the twin electromagnon is directly related to the presence of a magnetically induced oscillatory polarization in the ground state. This leads to the surprising prediction that TbMnO$_3$ has an oscillatory polarization with amplitude 50 times larger than its uniform polarization.