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Magneto-electric excitations in multiferroic TbMnO3 by Raman scattering

Low energy excitations in the multiferroic material TbMnO3 have been investigated by Raman spectroscopy. Our observations reveal the existence of two peaks at 30 cm-1 and 60 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 cm-1 excitation enhanced by the electric field of light along the spontaneous polarization. The origins of the modes are discussed under Raman and infrared selection rules considerations.