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L. Linhart, M. Paur, V. Smejkal, J. Burgdörfer, T. Müller, F. Libisch:
"Excitonic effects in strained TMDs and defects in graphene - a tight-binding approach";
Poster: Graphene week 2018, St. Sebastian; 09-10-2018 - 09-14-2018.

Single photon emitters (SPE) in WSe 2 have been investigated in several recent publications
[1, 2], receiving considerable attention in the field of two-dimensional materials. Although the
origin of these emitters is generally attributed to defects and/or local strain, an exact micro-
scopic explanation has proven elusive. Using a combination of a large set of SPE data and a
multi scale tight-binding model capturing non-uniform strain, defects and Hatree-interactions
we elucidate this mystery. We have measured over 500 SPE wrapped over nanopillars, found
clear antibunching signatures and a clear linear polarization of the observed SPE. Tight-binding
calculations with local strain patterns and open boundary conditions for a large WSe2 flake yield
quantum-dot-like localization. Including defects in the simulation yields qualitative agreement
of experimental and calculated linewidth distributions. We conclude that local strain shifts ex-
citonic energy levels into an energy of otherwise unoccupied inter-gap defect states, acting as a
doorkeeper to fill these states. Together with localized valence bands, this leads to sharp single
photon emitters.
[1] Koperski M., Nogajewski K. et.al., "Single photon emitters in exfoliated WSe 2 structures",
Nature Nanotechnology, 10, 503-605, (2015).
[2] Srivastava A., Sidler M. et.al., "Single-photon emission from localized excitons in an atomically
thin semiconductor", Nature Nanotechnology, 10, 491-496, (2015).