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

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

Wahib Aggoune, Klaus Irmscher, Dmitrii Nabok, Cecilia Vona, Saud Bin Anooz, Zbigniew Galazka, Martin Albrecht, and Claudia Draxl

Phys. Rev. B 103, 115105 – Published 3 March 2021

Abstract

We provide a combined theoretical and experimental study of the electronic structure and the optical absorption edge of the orthorhombic perovskite $La In O_{3}$ , 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 ( $Γ$ 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.

Received 11 January 2021
Revised 9 February 2021
Accepted 11 February 2021

DOI:https://doi.org/10.1103/PhysRevB.103.115105

Physics Subject Headings (PhySH)

Electronic structure Excitons

Transparent conducting oxides

Bethe-Salpeter equation Density functional theory Ellipsometry Green's function methods Optical absorption spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Wahib Aggoune ^1,*, Klaus Irmscher ², Dmitrii Nabok ^1,3, Cecilia Vona ^1,3, Saud Bin Anooz ², Zbigniew Galazka ², Martin Albrecht², and Claudia Draxl ^1,3

¹Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
²Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany
³European Theoretical Spectroscopic Facility (ETSF)

^*aggoune@physik.hu-berlin.de

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Vol. 103, Iss. 11 — 15 March 2021

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Figure 1
(a) Primitive cell (left) of orthorhombic $La In O_{3}$ and first Brillouin zone (right) with high-symmetry points and paths indicated in red; (b) PBEsol band structure with (orange) and without (black) spin-orbit coupling (SOC); (c) atomic characters projected onto the PBEsol band structure; (d) HSE06, and (e) $G_{0} W_{0}$ @HSE06 band structures. In all panels, the midgap is set to zero.
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Figure 2
(a) Band character projected onto the PBEsol band structure along the $Y - Γ - Z$ path in the Brillouin zone (BZ). The CB is shifted upwards by 2.13 eV to recover the $G_{0} W_{0}$ @HSE06 band gap. (c) Square modulus of the Kohn-Sham wave function (yellow) of the valence band maximum (VBM)/valence band (VB)-1, VB-2, VB-3, VB-4, VB-5, and conduction band minimum (CBm) states at $Γ$ , highlighted by black, green, orange, red, blue, and white circles, respectively, in the band structure shown in (b).
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Figure 3
(a) Imaginary part of the macroscopic dielectric function of $La In O_{3}$ for light polarization along [100] (blue), [010] (red), and [001] (green) direction as computed from the Bethe-Salpeter equation (BSE) (solid line). The independent quasiparticle approximation (IQPA) spectrum (shaded gray area) is shown for comparison. The position of the lowest-energy excitation $D$ is marked by a black triangle, and the ranges of weak excitations are highlighted with dashed rectangles (BSE spectra). (b) and (d) Band contributions to the weak and (c) first intense excitations. (e) Exciton wave function of excitation $C$ , showing the spatial electron distribution (green) with respect to the hole being fixed at an oxygen atom (yellow spot). The crystal structure is shown locally to ease the visualization.
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Figure 4
(a) Computed imaginary part of the macroscopic dielectric function of $La In O_{3}$ (solid lines), for light polarization oriented along the [100] (blue), [010] (red), and [001] (green) directions. The position of the lowest optical transitions ( $D$ ) is marked with a black triangle. The first intense excitation ([001] polarization) is indicated by the vertical green line, the electronic quasiparticle (QP) gap by the vertical black line. Corrections due to zero-point vibration (ZPV) and temperature effects are included to correspond to 300 K. Absorption spectrum taken at room temperature of a single $La In O_{3}$ crystal, obtained from (b) ellipsometry and (c) optical absorption. The corresponding onsets are highlighted with green (solid) and black (dashed) vertical lines, respectively. The experimental error bar is estimated to be $\sim 0.1$ eV, as indicated by the line thicknesses.
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Figure 5
Temperature dependence of the optical gap obtained by optical absorption measurements. Blue, red, and green symbols represent the measured data for light polarization along [100], [010], and [001], respectively; the corresponding solid lines are the best fits based on a single-oscillator model. The dashed green line shows a linear fit for high temperatures. The inset zooms into the low-temperature region to distinguish between gap renormalization due to temperature and zero-point vibration (ZPV).
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Physical Review B

covering condensed matter and materials physics

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

Wahib Aggoune, Klaus Irmscher, Dmitrii Nabok, Cecilia Vona, Saud Bin Anooz, Zbigniew Galazka, Martin Albrecht, and Claudia Draxl

Phys. Rev. B 103, 115105 – Published 3 March 2021

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Physical Review B

covering condensed matter and materials physics

Fingerprints of optical absorption in the perovskite LaInO3: Insight from many-body theory and experiment

Wahib Aggoune, Klaus Irmscher, Dmitrii Nabok, Cecilia Vona, Saud Bin Anooz, Zbigniew Galazka, Martin Albrecht, and Claudia Draxl

Phys. Rev. B 103, 115105 – Published 3 March 2021

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