Low-energy excitations in the multiferroic material ${\text{TbMnO}}_3$ have been investigated by Raman spectroscopy. Our observations reveal the existence of two peaks at 30 and $60{\text{cm}}^{-1}$. They are observed in the cycloidal phase below the Curie temperature but not in the sinusoidal phase, suggesting their magnetoelectric origin. While the peak energies coincide with the frequencies of electromagnons measured previously by transmission spectroscopy, they show surprisingly different selection rules, with the $30{\text{cm}}^{-1}$ excitation enhanced by the electric field of light along the spontaneous polarization. The origins of the two modes are discussed under Raman and infrared selection rules considerations.

• Received 30 November 2009

DOI:https://doi.org/10.1103/PhysRevB.81.054428