Many-body large polaron optical conductivity in SrTi$_{1-x}$Nb$_x$O$_3$

TL;DR

This paper models the optical conductivity of niobium-doped SrTiO$_{3}$ using a many-body large polaron framework that accounts for complex electron-phonon interactions and band structure effects, successfully explaining experimental spectra.

Contribution

It introduces a comprehensive many-body large-polaron theory for SrTi$_{1-x}$Nb$_{x}$O$_{3}$ that incorporates multiple phonon branches and band anisotropy, explaining experimental optical data without parameter adjustments.

Findings

The theory reproduces key features of the optical conductivity spectra.

It explains the peak at ~130 meV without parameter tuning.

The model highlights the importance of many-body effects in polaron behavior.

Abstract

Recent experimental data on the optical conductivity of niobium doped SrTiO$_{3}$ are interpreted in terms of a gas of large polarons with effective coupling constant $\alpha_{eff}\approx2$. The {theoretical approach takes into account} many-body effects, the electron-phonon interaction with multiple LO-phonon branches, and the degeneracy and the anisotropy of the Ti t$_{2g}$ conduction band. {Based on the Fr\"{o}hlich interaction, the many-body large-polaron theory} provides an interpretation for the essential characteristics, except -- interestingly -- for the unexpectedly large intensity of a peak at $\sim130$ meV, of the observed optical conductivity spectra of SrTi$_{1-x}$Nb$_{x}$O$_{3}$ \textit{without} any adjustment of material parameters.