Strain control of hybridization between dark and localized excitons in a 2D semiconductor

Photoluminescence imaging of single photon emitters within nanoscale strain profiles in monolayer WSe$_2$

“…These observations suggest that strain-induced trapping of bright excitons is an unlikely SPE formation mechanism in our experiment. Instead, they are consistent with the hypothesis that attributes SPE formation to the strain-induced resonant hybridization of optically dark excitons with point-like defects as discussed in recent works [23,24,41]. The proposed single-photon emission mechanism is schematically illustrated in Fig.…”

“…4c (right panel) supports this assignment as it is peaked near 1.63 eV corresponding to the expected spectral position of the midgap Se-vacancy defect [41]. The relatively large width of the SPE energy distribution agrees with the results of recent experimental studies on statistics of emitters in WS 2 monolayer [45,46] and reports on dark-localised exciton mixing in the wide spectral range around the defect energy level [41].…”

“…To enable the brightening process, the dark exciton (X 0 d , brown curve) should come in resonance with the defect level (green dashed line), which is achieved via strain-induced energy shift. While the energy of a defect level is almost independent of strain [41], the dark exciton energy follows the local variation of the band gap and matches the defect energy at certain values of total in-plane strain resulting in a possible photon emission event (wavy arrow).…”

“…However, brightening of intravalley dark excitons is less likely as it requires an additional spin flip process. The defects involved in the brightening process are likely the omnipresent Se vacancies [23], with corresponding energy levels lying several tens of meV below the dark exciton in monolayer WSe 2 [24,41]. Our experimentally measured distribution of SPE energies obtained from a large ensemble of > 80 emitters shown in Fig.…”

Conversion of Classical Light Emission from a Nanoparticle‐Strained WSe2 Monolayer into Quantum Light Emission via Electron Beam Irradiation

“…[17][18][19][20][21][22][23][24][25] More recent work builds upon this idea and proposes that point defects, such as atomic vacancies, in addition to strain, are essential to form SPEs. [26][27][28][29][30][31][32] Under these conditions, it is hypothesized that SPEs originate from the hybridization of the strained dark exciton band and a valley symmetry-breaking defect state. This model was recently supported in a study where the formation of SPEs was observed after applying both strain and electron beam (e − -beam) irradiation to WSe 2 .…”