Observation of quasi-steady dark excitons and gap phase in a doped semiconductor

Abstract

Exciton plays an important role in optics and optics-related behaviors and leads to novel correlated phases like charge order, exciton insulator, and exciton-polariton condensation. Dark exciton shows distinct properties from bright one. However, it cannot be directly detected by conventional optic measurements. The electronic modulation effect of dark excitons in quasi-equilibrium distribution, critical for electronic devices in working status, is still elusive. Here, using angle-resolved photoemission spectroscopy, we report creating, detecting, and controlling dark excitons in the quasi-equilibrium distribution in a doped semiconductor SnSe2. Surprisingly, we observe an excitonic gap phase, with a conduction band opening an anisotropic gap. Our results broaden the scope of dark excitons, extending their studies from the picosecond timescale in the ultrafast photoemission process to conditions occurring under quasi-equilibrium. We reveal the light-matter interaction in the engineering of electronic structures and provide a new way to realize the excitonic gap phase in semiconductors with large band gaps.

16 pages, 5 figures

References in corpus (16)

• Advanced capabilities for materials modelling with Quantum ESPRESSO
• High-temperature superfluidity with indirect excitons in van der Waals heterostructures
• Evidence for an excitonic insulator phase in 1T-TiSe${}_2$
• Layer-dependent properties of SnS2 and SnSe2 novel two-dimensional materials
• Directly visualizing the momentum forbidden dark excitons and their dynamics in atomically thin semiconductors
• Strength of the Spin-Fluctuation-Mediated Pairing Interaction in a High-Temperature Superconductor
• Spontaneous exciton condensation in 1T-TiSe2: a BCS-like approach
• Momentum-resolved observation of exciton formation dynamics in monolayer WS${}_2$
• Direct measurement of key exciton properties: energy, dynamics and spatial distribution of the wave function
• First-principles approach to excitons in time-resolved and angle-resolved photoemission spectra
• Evidences for the exciton gas phase and its condensation in monolayer 1T-ZrTe2
• Interaction-driven transport of dark excitons in 2D semiconductors with phonon-mediated optical readout
• Observation of possible excitonic charge density waves and metal-insulator transitions in atomically thin semimetals
• Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3
• Ultrafast generation and decay of a surface metal
• Anomalous normal state gap in an electron-doped cuprate