Electron-phonon coupling in Nb-doped SrTiO3 single crystal

Near normal incident infrared reflectivity spectra of (001) SrTi1-xNbxO3 single crystal have been measured at different temperatures in the frequency region between 100 and 6000 cm-1. The optical parameters of phonons and plasmons are obtained on the basis of the double-damping extended Drude model. The lowest frequency phonon mode at 175 cm-1 softens with decreasing temperature, and the plasmon frequency triples when the temperature decreases from 300 to 10 K. Extra absorption near the highest frequency longitudinal phonon mode shows that the effect of the polarons should be taken into account in addition to the plasmon-phonon coupling. The splitting of the last high reflectivity band, the temperature dependence of the 615 cm-1 structure and the appearance of a new weak peak-like defect mode provide evidence for the existence of small polarons