Here, ultra‐long lifetimes of defect‐trapped single quantum emitters (SQEs) in monolayer WSe2/hBN heterostructures are reported. The lifetimes of these SQEs are approximately 225 ns, more than two orders of magnitude larger than what has been previously reported for defect‐trapped excitons in WSe2. These SQEs consist of co‐linearly polarized doublet peaks with a fine structure splitting of 0.45 meV. Second‐order correlation measurements show antibunched single‐photon emission with a g(2)(0) value of ≈0.13. Through numerical analysis and modeling, it is shown how such long‐lifetime single emitters can arise from bright and dark exciton coupling in antisite defects on the W sites. Additionally, high‐quality single‐photon emission over a wide range of lifetimes—from 2 ns to over 200 ns—is also reported, suggesting a variety of other possible defect structures present. The flexibility to generate high fidelity single‐photon emission, over a wide range of lifetimes in a single material system, has potential in many optical quantum computing applications from high‐bit‐rate single‐photon sources to quantum memory devices.
In WSe2monolayers, strain has been used to control the energy of excitons, induce funneling, and realize single-photon sources. Here, we developed a technique for probing the dynamics of free excitons in nanoscale strain landscapes in such monolayers. A nanosculpted tapered optical fiber is used to simultaneously generate strain and probe the near-field optical response of WSe2monolayers at 5 K. When the monolayer is pushed by the fiber, its lowest energy states shift by as much as 390 meV (>20% of the bandgap of a WSe2monolayer). Polarization and lifetime measurements of these red-shifting peaks indicate they originate from dark excitons. We conclude free dark excitons are funneled to high-strain regions during their long lifetime and are the principal participants in drift and diffusion at cryogenic temperatures. This insight supports proposals on the origin of single-photon sources in WSe2and demonstrates a route towards exciton traps for exciton condensation.
more » « less- NSF-PAR ID:
- 10361589
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Solid‐state single photon emitters (SPEs) within atomically thin transition metal dichalcogenides (TMDs) have recently attracted interest as scalable quantum light sources for quantum photonic technologies. Among TMDs, WSe2monolayers (MLs) are promising for the deterministic fabrication and engineering of SPEs using local strain fields. The ability to reliably produce isolatable SPEs in WSe2is currently impeded by the presence of numerous spectrally overlapping states that occur at strained locations. Here nanoparticle (NP) arrays with precisely defined positions and sizes are employed to deterministically create strain fields in WSe2MLs, thus enabling the systematic investigation and control of SPE formation. Using this platform, electron beam irradiation at NP‐strained locations transforms spectrally overlapped sub‐bandgap emission states into isolatable, anti‐bunched quantum emitters. The dependence of the emission spectra of WSe2MLs as a function of strain magnitude and exposure time to electron beam irradiation is quantified and provides insight into the mechanism for SPE production. Excitons selectively funnel through strongly coupled sub‐bandgap states introduced by electron beam irradiation, which suppresses spectrally overlapping emission pathways and leads to measurable anti‐bunched behavior. The findings provide a strategy to generate isolatable SPEs in 2D materials with a well‐defined energy range.
-
more » « less
Abstract The monolayer transition metal dichalcogenides are an emergent semiconductor platform exhibiting rich excitonic physics with coupled spin-valley degree of freedom and optical addressability. Here, we report a new series of low energy excitonic emission lines in the photoluminescence spectrum of ultraclean monolayer WSe2. These excitonic satellites are composed of three major peaks with energy separations matching known phonons, and appear only with electron doping. They possess homogenous spatial and spectral distribution, strong power saturation, and anomalously long population (>6 µs) and polarization lifetimes (>100 ns). Resonant excitation of the free inter- and intravalley bright trions leads to opposite optical orientation of the satellites, while excitation of the free dark trion resonance suppresses the satellitesʼ photoluminescence. Defect-controlled crystal synthesis and scanning tunneling microscopy measurements provide corroboration that these features are dark excitons bound to dilute donors, along with associated phonon replicas. Our work opens opportunities to engineer homogenous single emitters and explore collective quantum optical phenomena using intrinsic donor-bound excitons in ultraclean 2D semiconductors.
-
more » « less
Abstract A comprehensive experimental study on optical properties and photocarrier dynamics in Bi2O2Se monolayers and nanoplates is presented. Large and uniform Bi2O2Se nanoplates with various thicknesses down to the monolayer limit are fabricated. In nanoplates, a direct optical transition near 720 nm is identified by optical transmission, photoluminescence, and transient absorption spectroscopic measurements and is attributed to the transition between the valence and conduction bands in the Γ valley. Time‐resolved differential reflection measurements reveal ultrafast carrier thermalization and energy relaxation processes and a photocarrier recombination lifetime of about 200 ps in nanoplates. Furthermore, by spatially resolving the differential reflection signal, a photocarrier diffusion coefficient of about 4.8 cm2s−1is obtained, corresponding to a mobility of about 180 cm2V−1s−1. A similar direct transition is also observed in monolayer Bi2O2Se, suggesting that the states in the Γ valley do not change significantly with the thickness. The temporal dynamics of the excitons in the monolayer is quite different from the nanoplates, with a strong saturation effect and fast exciton–exciton annihilation at high densities. Spatially and temporally resolved measurements yield an exciton diffusion coefficient of about 20 cm2s−1.
-
more » « less
Abstract Excitons are elementary optical excitation in semiconductors. The ability to manipulate and transport these quasiparticles would enable excitonic circuits and devices for quantum photonic technologies. Recently, interlayer excitons in 2D semiconductors have emerged as a promising candidate for engineering excitonic devices due to their long lifetime, large exciton binding energy, and gate tunability. However, the charge-neutral nature of the excitons leads to weak response to the in-plane electric field and thus inhibits transport beyond the diffusion length. Here, we demonstrate the directional transport of interlayer excitons in bilayer WSe2driven by the propagating potential traps induced by surface acoustic waves (SAW). We show that at 100 K, the SAW-driven excitonic transport is activated above a threshold acoustic power and reaches 20 μm, a distance at least ten times longer than the diffusion length and only limited by the device size. Temperature-dependent measurement reveals the transition from the diffusion-limited regime at low temperature to the acoustic field-driven regime at elevated temperature. Our work shows that acoustic waves are an effective, contact-free means to control exciton dynamics and transport, promising for realizing 2D materials-based excitonic devices such as exciton transistors, switches, and transducers up to room temperature.
