We propose a model for the pair of electromagnon excitations observed in the class of multiferroic materials {\it R}MnO3 ({\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 TbMnO3 has an oscillatory polarization with amplitude 50 times larger than its uniform polarization.
@article{arxiv.0906.3059,
title = {Model for twin electromagnons and magnetically induced oscillatory polarization in multiferroic RMnO$_3$},
author = {Markku P. V. Stenberg and Rogerio de Sousa},
journal= {arXiv preprint arXiv:0906.3059},
year = {2009}
}