Raman evidence for Orbiton-Mediated Multiphonon Scattering in Multiferroic TbMnO${}_3$

Abstract

Temperature-dependent Raman spectra of TbMnO${}_3$ from 5 K to 300 K in the spectral range of 200 to 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 ($\sim$ 0.6) at all temperatures, suggesting a orbiton-phonon mixed nature of the high frequency mode. One of the first order phonon modes shows anomalous softening below T${}_N$ ($\sim$ 46 K), suggesting a strong spin-phonon coupling.

14 pages, 3 figures, 1 table