Domain fluctuations near the field-induced incommensurate-commensurate phase transition of TbMnO3

We present temperature- and field-dependent inelastic light-scattering studies of multiferroic TbMnO3. By carefully examining the evolution of magneto-elastic modes in various phases of TbMnO3, our study reveals several features of the field-induced incommensurate-commensurate (IC-C) transition in TbMnO3. We find that, for fields applied along the b axis, there is a coexistence of distinct structural phases in the intermediate field regime (H=4-7 T) around the IC-C-phase transition. We present evidence for the existence of dynamical fluctuations of the C phase for fields lower than the critical field for H along the b axis, H < H-c(b). Furthermore, we present evidence for strong spin-lattice coupling effects in TbMnO3 in the form of zone-boundary phonon modes that strongly couple to the spins by modulating the exchange interaction in this material.