Strongly bound excitons in anatase TiO2 single crystals and nanoparticles

Abstract

Anatase TiO${}_2$ is among the most studied materials for light-energy conversion applications, but the nature of its fundamental charge excitations is still unknown. Yet it is crucial to establish whether light absorption creates uncorrelated electron-hole pairs or bound excitons and, in the latter case, to determine their character. Here, by combining steady-state angle-resolved photoemission spectroscopy and spectroscopic ellipsometry with state-of-the-art ab initio calculations, we demonstrate that the direct optical gap of single crystals is dominated by a strongly bound exciton rising over the continuum of indirect interband transitions. This exciton possesses an intermediate character between the Wannier-Mott and Frenkel regimes and displays a peculiar two-dimensional wavefunction in the three-dimensional lattice. The nature of the higher-energy excitations is also identified. The universal validity of our results is confirmed up to room temperature by observing the same elementary excitations in defect-rich samples (doped single crystals and nanoparticles) via ultrafast two-dimensional deep-ultraviolet spectroscopy.

References in corpus (16)

• Observation of giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
• Optical Spectrum of MoS${}_2$: Many-body Effects and Diversity of Exciton States
• Tightly bound excitons in monolayer WSe2
• Yambo: an \textit{ab initio} tool for excited state calculations
• BerkeleyGW: A Massively Parallel Computer Package for the Calculation of the Quasiparticle and Optical Properties of Materials and Nanostructures
• A direct view at excess electrons in TiO${}_2$ rutile and anatase
• Tunable polaronic conduction in anatase TiO2
• A precise method for visualizing dispersive features in image plots
• Self-Energy and Excitonic Effects in the Electronic and Optical Properties of TiO2 Crystalline Phases
• One-shot calculation of temperature-dependent optical spectra and phonon-induced band-gap renormalization
• Quasiparticle and Optical Properties of Rutile and Anatase TiO${}_2$
• Correlation effects on electron-phonon coupling in semiconductors: many-body theory along thermal lines
• Optical to UV spectra and birefringence of SiO${}_2$ and TiO${}_2$: First-principles calculations with excitonic effects
• Renormalization of the Optical Response of Semiconductors by Electron-Phonon Interaction
• Anisotropic excitonic effects in the energy loss function of hexagonal boron nitride
• Optical probe of ferroelectric order in bulk and thin film perovskite titanates

Cited by in corpus (16)

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• First-principles Hubbard U and Hund's J corrected approximate density-functional theory predicts an accurate fundamental gap in rutile and anatase TiO2
• Optical excitations and thermoelectric properties of 2D holey graphene
• Self energy and excitonic effect in (un)doped TiO${}_2$ anatase : A comparative study of hybrid DFT, GW and BSE to explore optical properties
• X-ray Absorption Linear Dichroism at the Ti K-edge of TiO2 anatase single crystals
• Phonon-Driven Selective Modulation of Exciton Oscillator Strengths in Anatase TiO2 Nanoparticles
• Hund's coupling driven photo-carrier relaxation in the two-band Mott insulator
• Role of Quantum-Confinement in Anatase Nanosheets
• Delocalization of dark and bright excitons in flat-band materials and the optical properties of V${}_2$O${}_5$
• Lattice-Mediated Magnetic Order Melting in TbMnO3
• Giant exciton Mott density in anatase TiO2
• Identification of large polarons and exciton polarons in rutile and anatase polymorphs of titanium dioxide
• Anomalous Anisotropic Exciton Temperature Dependence in Rutile TiO2
• Ab initio insights on the ultrafast strong-field dynamics of anatase TiO${}_2$
• Two-particle excitations under coexisting electron interaction and disorder
• Predicting the suitability of photocatalysts for water splitting using Koopmans spectral functionals: The case of TiO${}_2$ polymorphs