Detecting photoelectrons from spontaneously formed excitons

Abstract

Excitons, quasiparticles of electrons and holes bound by Coulombic attraction, are created transiently by light and play an important role in optoelectronics, photovoltaics and photosynthesis. While they are also predicted to form spontaneously in a small gap semiconductor or a semimetal, leading to a Bose-Einstein condensate at low temperature, their material realization has been elusive without any direct evidence. Here we detect the direct photoemission signal from spontaneously formed excitons in a debated excitonic insulator candidate Ta2NiSe5. Our symmetry-selective angle-resolved photoemission spectroscopy reveals a characteristic excitonic feature above the transition temperature, which provides detailed properties of excitons such as anisotropic Bohr radius. The present result evidences so called preformed excitons and guarantees the excitonic insulator nature of Ta2NiSe5 at low temperature. Direct photoemission can be an important tool to characterize steady-state excitons.

References in corpus (38)

• Restoring the density-gradient expansion for exchange in solids and surfaces
• Generalized gradient approximation for solids and their surfaces
• Angle-resolved photoemission spectroscopy of the cuprate superconductors
• Atomically thin p-n junctions with van der Waals heterointerfaces
• Electrically Tunable Excitonic Light Emitting Diodes based on Monolayer WSe2 p-n Junctions
• Photovoltaic effect in an electrically tunable van der Waals heterojunction
• Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors
• Evidence of high-temperature exciton condensation in 2D atomic double layers
• Macroscopically ordered state in exciton system
• Signatures of exciton condensation in a transition metal dichalcogenide
• Quantum Hall Drag of Exciton Superfluid in Graphene
• Orthorhombic-to-Monoclinic Phase Transition of Ta2NiSe5 Induced by the Bose-Einstein Condensation of Excitons
• Excitonic Bose-Einstein condensation in Ta2NiSe5 above room temperature
• Macroscopic coherence of a single exciton state in a polydiacetylene organic quantum wire
• Spontaneous exciton condensation in 1T-TiSe2: a BCS-like approach
• Coherent Order Parameter Oscillations in the Ground State of the Excitonic Insulator Ta2NiSe5
• On the possibility of an excitonic insulator at the semiconductor-semimetal transition
• Nature of symmetry breaking at the excitonic insulator transition: Ta${}_2$NiSe${}_5$
• Transient excitons at metal surfaces
• Giant exciton Fano resonance in quasi-one-dimensional Ta${}_2$NiSe${}_5$
• Photo-induced semimetallic states realised in electron-hole coupled insulators
• Electron-hole pair condensation at the semimetal-semiconductor transition: a BCS-BEC crossover scenario
• Strong Coupling Nature of the Excitonic Insulator State in Ta${}_2$NiSe${}_5$
• Direct observation of excitonic instability in Ta2NiSe5
• A BCS-BEC crossover in the extended Falicov-Kimball model: Variational cluster approach
• Electron-Phonon Coupling Mode in Excitonic Insulator
• Photoemission signature of excitons
• Theory of exciton dynamics in time-resolved ARPES: intra- and intervalley scattering in two-dimensional semiconductors
• Band hybridisation at the semimetal-semiconductor transition of Ta${}_2$NiSe${}_5$ enabled by mirror-symmetry breaking
• Strong interband interaction in the excitonic insulator phase of Ta${}_2$NiSe${}_5$
• Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ at room temperature
• Fate of the excitonic insulator in the presence of phonons
• Ultrafast melting and recovery of collective order in the excitonic insulator Ta${}_2$NiSe${}_5$
• Orthorhombic-to-monoclinic transition in Ta${}_2$NiSe${}_5$ due to a zone-center optical phonon instability
• Phononic soft mode and strong electronic background behavior across the structural phase transition in the excitonic insulator Ta${}_2$NiSe${}_5$ (with Erratum)
• Infrared phonon spectra of quasi-one-dimensional Ta${}_2$NiSe${}_5$ and Ta${}_2$NiS${}_5$
• Dynamics of incoherent exciton formation in Cu${}_2$O: Time- and angle-resolved photoemission spectroscopy
• The spontaneous symmetry breaking in Ta${}_2$NiSe${}_5$ is structural in nature

Cited by in corpus (10)

• Evidences for the exciton gas phase and its condensation in monolayer 1T-ZrTe2
• Excitonic Condensate in Flat Valence and Conduction Bands of Opposite Chirality
• Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5
• Disentangling lattice and electronic instabilities in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ by nonequilibrium spectroscopy
• Terahertz parametric amplification as a reporter of exciton condensate dynamics
• Pressure suppression of the excitonic insulator state in Ta2NiSe5 observed by optical conductivity
• Third-harmonic generation in excitonic insulators
• Spectral signatures of a unique charge density wave in Ta${}_2$NiSe${}_7$
• Coherence and de-coherence in the Time-Resolved ARPES of realistic materials: an ab-initio perspective
• Electronic band structure in pristine and Sulfur-doped Ta${}_2$NiSe${}_5$