Large polaron evolution in anatase TiO2 due to carrier and temperature dependence of electron-phonon coupling

TL;DR

This study investigates how carrier concentration and temperature influence electron-phonon interactions and polaron behavior in anatase TiO2, revealing unusual mobility trends and detailed transport mechanisms.

Contribution

It provides a comprehensive phase diagram linking polaron characteristics with transport properties in anatase TiO2, highlighting the role of screening effects.

Findings

Mobility increases with carrier concentration due to screening of e-ph coupling.

Magnetoresistance decomposes into linear and quadratic components, indicating different carrier behaviors.

A unified phase diagram clarifies the large polaron nature in anatase TiO2.

Abstract

The electronic and magneto transport properties of reduced anatase TiO2 epitaxial thin films are analyzed considering various polaronic effects. Unexpectedly, with increasing carrier concentration, the mobility increases, which rarely happens in common metallic systems. We find that the screening of the electron-phonon (e-ph) coupling by excess carriers is necessary to explain this unusual dependence. We also find that the magnetoresistance (MR) could be decomposed into a linear and a quadratic component, separately characterizing the transport and trap behavior of carriers as a function of temperature. The various transport behaviors could be organized into a single phase diagram which clarifies the nature of large polaron in this material.