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F. Libisch:
"Localized inter-valley defect excitons as single-photon emitters in WSe2";
Vortrag: Seminarvortrag, Neapel, Italien (eingeladen); 03.06.2019.

Single-photon emitters play a key role in present and emerging quantum technologies.
Several recent measurements have established monolayer WSe2 as a promising candidate for
a reliable single photon source. The origin and underlying microscopic processes have
remained, however, largely elusive. We present a multi-scale tight-binding simulation for the
optical spectra of WSe2 under non-uniform strain and in the presence of point defects
employing the Bethe-Salpeter equation. Strain locally shifts excitonic energy levels into the
band gap where they overlap with localized intra-gap defect states. The resulting
hybridization allows for efficient filing and subsequent radiative decay of the defect states.
We identify inter-valley defect excitonic states as the likely candidate for anti-bunched
single-photon emission. This proposed scenario is shown to account for a large variety of
experimental observations including brightness, radiative transition rates, the variation of the
excitonic energy with applied magnetic and electric fields as well as the variation of the
polarization of the emitted photon with the magnetic field.