Delocalization of dark and bright excitons in flat-band materials and the optical properties of V${}_2$O${}_5$

Abstract

The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons, where electrons and holes stay close together, which is associated with a large binding energy. Here, using the example of the layered oxide V${}_2$O${}_5$ , we show how localized charge-transfer excitations combine to form excitons that also have a huge binding energy but, at the same time, a large electron-hole distance, and we explain this seemingly contradictory finding. The anisotropy of the exciton delocalization is determined by the local anisotropy of the structure, whereas the exciton extends orthogonally to the chains formed by the crystal structure. Moreover, we show that the bright exciton goes together with a dark exciton of even larger binding energy and more pronounced anisotropy. These findings are obtained by combining first principles many-body perturbation theory calculations, ellipsometry experiments, and tight binding modelling, leading to very good agreement and a consistent picture. Our explanation is general and can be extended to other materials.

References in corpus (24)

• Rediscovering Black Phosphorus: A Unique Anisotropic 2D Material for Optoelectronics and Electronics
• Excitons in atomically thin transition metal dichalcogenides
• The GW method
• Quasiparticle Self-Consistent GW Theory
• Ab initio calculation of excitonic effects in the optical spectra of semiconductors
• Excitonic Effects on the Optical Response of Graphene and Bilayer Graphene
• Giant Piezoelectricity in Monolayer Group IV Monochalcogenides: SnSe, SnS, GeSe and GeS
• Dielectric screening in two-dimensional insulators: Implications for excitonic and impurity states in graphane
• Magnetic brightening and control of dark excitons in monolayer WSe2
• Radiative control of dark excitons at room temperature by nano-optical antenna-tip induced Purcell effect
• NaV_2O_5 as a quarter-filled ladder compound
• Dark excitons in transition metal dichalcogenides
• Implementation of an all-electron GW approximation based on the PAW method without plasmon pole approximation: application to Si, SiC, AlAs, InAs, NaH and KH
• Strongly bound excitons in anatase TiO2 single crystals and nanoparticles
• Physical origin of giant excitonic and magneto-optical responses in two-dimensional ferromagnetic insulators
• Exciton band structure in two-dimensional materials
• Charge ordering and opening of spin gap in NaV_2O_5
• Automation methodologies and large-scale validation for $GW$, towards high-throughput $GW$ calculations
• Accurate energy bands calculated by the hybrid quasiparticle self-consistent GW method implemented in the ecalj package
• Excitonic structure of the optical conductivity in MoS${}_2$ monolayers
• Valence band electronic structure of V2O3: identification of V and O bands
• Valence band excitations in V_2O_5
• Anomalous Non-Hydrogenic Exciton Series in 2D Materials on High-$\kappa$ Dielectric Substrates
• Ultrathin 2D-oxides: a perspective on fabrication, structure, defect, transport, electron and phonon properties

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• Robustness of electronic screening effects in electron spectroscopies: example of V${}_2$O${}_5$
• Optical absorption and luminescence of $\alpha$-LiV${}_2$O${}_5$ from the Bethe Salpeter Equation
• High-throughput study of kagome compounds in the AV3Sb5 family
• On the origin of bulk-related anisotropies in surface optical spectra