Temperature (5--250 K) and magnetic field (0--70 kOe) variations of the low-energy (1--10 meV) electrodynamics of spin excitations have been investigated for a complete set of light-polarization configurations for a ferroelectric magnet DyMnO3 by using terahertz time-domain spectroscopy. We identify the pronounced absorption continuum (1--8 meV) with a peak feature around 2 meV, which is electric-dipole active only for the light E-vector along the a-axis. This absorption band grows in intensity with lowering temperature from the spin-collinear paraelectric phase above the ferroelectric transition, but is independent of the orientation of spiral spin plane (bc or ab), as shown on the original Ps (ferroelectric polarization) ∥c phase as well as the magnetic field induced Ps∥a phase. The possible origin of this electric-dipole active band is argued in terms of the large fluctuations of spins and spin-current.
@article{arxiv.0711.2733,
title = {Electrically driven spin excitation in a ferroelectric magnet DyMnO_3},
author = {N. Kida and Y. Ikebe and Y. Takahashi and J. P. He and Y. Kaneko and Y. Yamasaki and R. Shimano and T. Arima and N. Nagaosa and Y. Tokura},
journal= {arXiv preprint arXiv:0711.2733},
year = {2009}
}