Photon superbunching in cathodoluminescence of excitons in WS₂monolayer

Abstract

Cathodoluminescence spectroscopy in conjunction with second-order auto-correlation measurements of g_2(τ) allows to extensively study the synchronization of photon emitters in low-dimensional structures. Co-existing excitons in two-dimensional transition metal dichalcogenide monolayers provide a great source of identical photon emitters which can be simultaneously excited by an electron. Here, we demonstrate large photon bunching with g_2(0) up to 156±16 of a tungsten disulfide monolayer (WS2), exhibiting a strong dependence on the electron-beam current. To further improve the excitation synchronization and the electron-emitter interaction, we show exemplary that the careful selection of a simple and compact geometry -- a thin, monocrystalline gold nanodisk -- can be used to realize a record-high bunching g_2(0) of up to 2152±236. This approach to control the electron excitation of excitons in a WS2 monolayer allows for the synchronization of photon emitters in an ensemble, which is important to further advance light information and computing technologies.

Cathodoluminescence spectroscopy of monolayer hexagonal boron nitride

“…However, CL signals of the hBN flakes thinner than 5 layers have not been shown due presumably to the small excitation volume of ultrathin hBN films including mBN and to the finite depth of the projected range of an e -beam in the CL system equipped on the scanning electron microscopy (SEM), which gave rise to the surface-insensitive excitation. Here we note that, for the cases of monolayer TMDs, CL signals have been recorded only when the monolayer TMDs have been encapsulated with hBN layers, where the wide E g hBN layer functioned as an e-beam absorber for increasing the number of excited carriers that were injected in the monolayer TMDs 31 – 36 . However, such artificial vdW structures 31 – 36 are not feasible when measuring an mBN itself.…”

“…Here we note that, for the cases of monolayer TMDs, CL signals have been recorded only when the monolayer TMDs have been encapsulated with hBN layers, where the wide E g hBN layer functioned as an e-beam absorber for increasing the number of excited carriers that were injected in the monolayer TMDs 31 – 36 . However, such artificial vdW structures 31 – 36 are not feasible when measuring an mBN itself.…”

Giant Superbunching Emission from Mesoscopic Perovskite Emitter Clusters

“…[26,[44][45][46]55] To fully understand the observations, more theoretical efforts are needed, here we note a new theoretical work about superbunching emission in the cathodoluminescence (CL) process as CL usually gives huge g (2) (0). [56][57][58] Recently, Yuge et al [59] proposed a model of quantum master equation to describe the dynamics of multiple emitters in CL. Their model successfully reproduces several features of CL, particularly the superbunching and decaying behavior of g (2) (𝜏).…”

Cathodoluminescence Nanoscopy: State of the Art and Beyond

“…Nevertheless, the CL-measured g (2) (Δt) of multiple defect centers shows strong photon bunching (Figure 5b) in contrast to PL-measured g (2) (Δt). 34,135,136 This bunching behavior originates from the synchronized emission from multiple centers excited by the same electron through the cascade decay. More recently, an experimental demonstration of the crossover between the bunching and antibunching regimes was provided by varying the electron-beam current in the CL study of color centers in diamond crystals, 137 confirming the tunability of photon-correlation statistics in CL predicted by Meuret et al 135 Based on a developed statistical model that determines the bunching strength g (2) (0) from the electron beam current, emitter decay lifetime, and electron excitation efficiency, the precise measurements of photon bunching permit retrieving the information about lifetime and excitation/emission efficiency of emitters with a high spatial resolution.…”