Electron-phonon interaction and charge carrier mass enhancement in SrTiO3

TL;DR

This study investigates the electron-phonon interactions in Nb-doped SrTiO3, revealing a significant mass enhancement due to electron-phonon coupling without forming small polarons, and quantifying the coupling strength.

Contribution

It provides a comprehensive optical and transport analysis of SrTiO3, quantifying the electron-phonon coupling strength and its effect on charge carrier mass enhancement.

Findings

Approximately threefold increase in band mass observed.

Spectral weight transferred to a mid-infrared band from electron-phonon interactions.

Electron-phonon coupling parameter estimated at about 4, indicating intermediate coupling strength.

Abstract

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, $\alpha \approx 4$.