Raman evidence for orbiton-mediated multiphonon scattering in multiferroic TbMnO₃

Temperature-dependent Raman spectra of TbMnO(3) from 5 to 300 K in the spectral range of 200-1525 cm(-1) show five first-order Raman allowed modes and two high frequency modes. The intensity ratio of the high frequency Raman band to the corresponding first-order Raman mode is nearly constant and high (∼0.6) at all temperatures, suggesting an orbiton-phonon mixed nature of the high frequency mode. One of the first-order phonon modes shows anomalous softening below T(N) (∼46 K), suggesting a strong spin-phonon coupling.