We provide a combined theoretical and experimental study of the electronic structure and the optical absorption edge of the orthorhombic perovskite $\mathrm{La}\mathrm{In}{\mathrm{O}}_3$, employing density functional theory and many-body perturbation theory. We find the lowest-energy excitation at 0.2 eV below the fundamental gap (5 eV), reflecting a sizable electron-hole attraction. Since the transition from the valence band maximum ($\mathrm{\Gamma }$ 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 well enough resolved by the ellipsometry measurement. Through temperature-dependent measurements of the optical gap, we assess renormalization effects by electron-phonon coupling, enhancing the quantitative comparison between theoretical and experimental results.

中文翻译：

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钙钛矿LaInO3中光吸收的指纹：多体理论和实验的见解

我们提供了正交晶体钙钛矿的电子结构和光吸收边缘的理论和实验组合研究 $\mathrm{啦啦}在{\mathrm{Ø}}_3$，运用密度泛函理论和多体摄动理论。我们发现在低于基本能隙（5 eV）的0.2 eV处的最低能量激发，反映出相当大的电子-空穴吸引。自从价带最大跃迁（$\mathrm{\Gamma }$点），但是，偶极子被禁止，其开始的特征是围绕它的跃迁产生的弱激励。第一次强烈激发出现在大约0.32 eV以上。有趣的是，该值与通过椭圆光度法（4.80 eV）获得的实验值一致，该实验值高于从光吸收光谱法获得的实验值（4.35 eV）。后者的差异归因于以下事实：椭偏测量无法很好地解决定义光学间隙的弱跃迁。通过光学间隙的温度相关测量，我们通过电子-声子耦合评估重归一化效应，从而增强了理论和实验结果之间的定量比较。