# Localized inter-valley defect excitons as single-photon emitters in WSe$_2$

## TL;DR

This paper uses multi-scale simulations to show that inter-valley defect excitons in strained WSe$_2$ can act as reliable single-photon emitters, explaining various experimental observations.

## Contribution

It introduces a detailed theoretical model linking defect states and strain to single-photon emission in WSe$_2$, clarifying the microscopic origin of these emitters.

## Key findings

- Inter-valley defect excitons are likely responsible for single-photon emission.
- Strain and defects hybridize excitonic states, enabling radiative decay.
- The model explains experimental variations under magnetic and electric fields.

## Abstract

Single-photon emitters play a key role in present and emerging quantum technologies. Several recent measurements have established monolayer WSe$_2$ 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 WSe$_2$ 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.