title: Evidence for an electric-dipole active continuum band of spin excitations in multiferroic TbMnO3.
abstract: The wide range optical spectra on a multiferroic prototype TbMnO3 have been investigated to clarify the origin of spin excitations observed in the far-infrared region. We elucidate the full band structure, whose high energy edge (133 cm;{-1}) exactly corresponds to twice of the highest-lying magnon energy. Thus the origin of this absorption band is clearly assigned to two-magnon excitation driven by the electric field of light. There is an overlap between the two-magnon and phonon energy ranges, where the strong coupling between them is manifested by the frequency shift and transfer of oscillator strength of the phonon mode.
authors.affiliation: Multiferroics Project, ERATO, Japan Science and Technology Agency (JST), Japan c/o Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Takahashi
authors.forename: N
authors.initials: N
authors.lastname: Kida
authors.forename: Y
authors.initials: Y
authors.lastname: Yamasaki
authors.forename: J
authors.initials: J
authors.lastname: Fujioka
authors.forename: T
authors.initials: T
authors.lastname: Arima
authors.forename: R
authors.initials: R
authors.lastname: Shimano
authors.forename: S
authors.initials: S
authors.lastname: Miyahara
authors.forename: M
authors.initials: M
authors.lastname: Mochizuki
authors.forename: N
authors.initials: N
authors.lastname: Furukawa
authors.forename: Y
authors.initials: Y
authors.lastname: Tokura