Interband and polaronic excitations in YTiO3 from first principles

TL;DR

This study re-evaluates the electronic structure of YTiO3, revealing that optical absorption onset is due to polaronic excitations rather than interband transitions, with implications for understanding its optical properties.

Contribution

The paper demonstrates that polaronic excitations, not interband transitions, dominate the optical absorption in YTiO3, challenging previous interpretations based on experimental data.

Findings

Interband transitions are higher in energy than the optical absorption onset.

Small polarons form in p-type doped YTiO3, leading to infrared absorption.

Polaronic excitations explain the experimental optical spectra.

Abstract

YTiO3, as a prototypical Mott insulator, has been the subject of numerous experimental investigations of its electronic structure. The onset of absorption in optical conductivity measurements has generally been interpreted to be due to interband transitions at the fundamental gap. Here we re-examine the electronic structure of YTiO3 using density functional theory with either a Hubbard correction (DFT+U) or a hybrid functional. Interband transitions turn out to be much higher in energy than the observed onset of optical absorption. However, in case of $p$-type doping, holes tend to become self-trapped in the form of small polarons, localized on individual Ti sites. Exciting electrons from the occupied lower Hubbard band to the small-polaron state then leads to broad infrared absorption, consistent with the onset in the experimental optical conductivity spectra.