Fingerprints of optical absorption in the perovskite LaInO$_{3}$: Insight from many-body theory and experiment

TL;DR

This study combines theory and experiment to analyze the electronic structure and optical absorption of LaInO₃, revealing a fundamental band gap of 4.55 eV and insights into excitonic effects and temperature dependence.

Contribution

It provides the first combined theoretical and experimental analysis of LaInO₃'s optical properties, including accurate band gap and excitonic effects, advancing understanding of its electronic structure.

Findings

Predicted a 5 eV quasiparticle band gap.

Identified a 0.2 eV excitonic binding energy.

Measured a 120 meV redshift of the optical gap with temperature.

Abstract

We provide a combined theoretical and experimental study of the electronic structure and the optical absorption edge of the orthorhombic perovskite LaInO$_{3}$. Employing density-functional theory and many-body perturbation theory, we predict a direct electronic quasiparticle band gap of about 5 eV and an effective electron (hole) mass of 0.31 (0.48) m$_{0}$. We find the lowest-energy excitation at 0.2 eV below the fundamental gap, reflecting a sizeable electron-hole attraction. Since the transition from the valence band maximum (VBM, $\Gamma$ point) is, however, dipole forbidden the onset is characterized by weak excitations from transitions around it. The first intense excitation appears about 0.32 eV above. Interestingly, this value coincides with an experimental value obtained by ellipsometry (4.80 eV) which is higher than the onset from optical absorption spectroscopy (4.35 eV). The latter discrepancy is attributed to the fact that the weak transitions that define the optical gap are not resolved by the ellipsometry measurement. The absorption edge shows a strong dependency on the light polarization, reflecting the character of the involved valence states. Temperature-dependent measurements show a redshift of the optical gap by about 120 meV by increasing the temperature from 5 to 300 K. Renormalization due to zero-point vibrations is extrapolated from the latter measurement to amount to 150 meV. By adding the excitonic binding energy of 0.2 eV obtained theoretically to the experimental optical absorption onset, we determine the fundamental band gap at room temperature to be 4.55 eV.