Raman study of orbital mediated multiphonons in RMnO<Subscript>3</Subscript> (R=Pr,Sm,Eu,Tb,Y)

We have studied RMnO<Subscript>3</Subscript> manganites (R=Pr, Sm, Eu, Tb, Y) Raman excitations in the 200–2800 cm<Superscript>-1</Superscript> range as a function of temperature. Combinations of phonon energies are observed up to the fourth order, indicating the presence of electron-phonon coupling. In comparison to Γ-point phonon combinations, double phonon excitations appear to be blue shifted in large size rare earth ion compounds. The phonon combination intensities decrease rapidly with their increasing order, confirming other studies which conclude that the electron-phonon coupling is not as strong as supposed in the localized limit. Moreover, different intensity order dependences are observed between the phonon combination and the so-called Jahn-Teller mode. These effects are better described in the orbiton-phonon coupling scheme. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006