We report a comprehensive THz, infrared and optical study of Nb doped SrTiO3 as well as DC conductivity and Hall effect measurements. Our THz spectra at 7K show the presence of a very narrow (<2 meV) Drude peak, the spectral weight of which shows approximately a factor of three enhancement of the band mass for all carrier concentrations. The missing spectral weight is regained in a broad 'mid-infrared' band which originates from electron-phonon coupling. We find no evidence of a particularly large electron-phonon coupling that would result in small polaron formation. Analysis of the results yields an electron-phonon coupling parameter of an intermediate strength, α≈4.
@article{arxiv.0712.1607,
title = {Electron-phonon interaction and charge carrier mass enhancement in SrTiO3},
author = {J. L. M. van Mechelen and D. van der Marel and C. Grimaldi and A. B. Kuzmenko and N. P. Armitage and N. Reyren and H. Hagemann and I. I. Mazin},
journal= {arXiv preprint arXiv:0712.1607},
year = {2009}
}