Observation of the effects of phonon dispersion on the Fröhlich-interaction-induced second-order Raman scattering in Pb2Sr2PrCu3O8

The one- and two-phonon Raman-scattering spectrum of single-crystal Pb2Sr2PrCu3O8 is examined under resonance conditions. Strong features appear in the one-phonon spectrum at the positions of longitudinal optical (LO) infrared modes as the laser energy approaches that of the charge transfer gap. These Fröhlich-interaction-induced modes are accompanied by a second-order spectrum composed of overtones and combinations of the LO and ordinary …