A consistent picture of excitations in cubic BaSnO$_{3}$ revealed by combining theory and experiment

TL;DR

This study combines advanced theoretical calculations with high-resolution experimental techniques to provide a comprehensive understanding of the electronic excitations and optical properties of cubic BaSnO$_{3}$, resolving previous controversies.

Contribution

It offers a fully consistent picture of BaSnO$_{3}$'s electronic structure by integrating ab initio methods with electron energy-loss spectroscopy and optical measurements, highlighting phonon-mediated indirect transitions.

Findings

Excellent agreement between theory and experiment on band gaps and effective masses.

Identification of weak excitations below the optical gap due to indirect transitions.

Confirmation of phonon-mediated symmetry lowering activating indirect transitions.

Abstract

Among the transparent conducting oxides, the perovskite barium stannate is most promising for various electronic applications due to its outstanding carrier mobility achieved at room temperature. However, most of its important characteristics, such as band gaps, effective masses, and absorption edge, remain controversial. Here, we provide a fully consistent picture by combining state-of-the-art {\it ab initio} methodology with forefront electron energy-loss spectroscopy and optical absorption measurements. Valence electron energy-loss spectra, featuring signals originating from band gap transitions, are acquired on defect-free sample regions of a BaSnO$_{3}$ single crystal. These high-energy-resolution measurements are able to capture also very weak excitations below the optical gap, attributed to indirect transitions. By temperature-dependent optical absorption measurements, we assess band-gap renormalization effects induced by electron-phonon coupling. Overall, we find for the effective electronic mass, the direct and the indirect gap, the optical gap, as well as the absorption onsets and spectra, excellent agreement between both experimental techniques and the theoretical many-body results, supporting also the picture of a phonon-mediated mechanism where indirect transitions are activated by phonon-induced symmetry lowering. This work demonstrates a fruitful connection between different high-level theoretical and experimental methods for exploring the characteristics of advanced materials.