Temperature dependent temporal coherence of metallic-nanoparticle-induced single-photon emitters in a WSe₂ monolayer

In recent years, much research has been undertaken to investigate the suitability of two-dimensional materials to act as single-photon sources with high optical and quantum optical quality. Amongst them, transition-metal dichalcogenides, especially WSe2, have been one of the subjects of intensive studies. Yet, their single-photon purity and photon indistinguishability remain the most significant challenges to compete with mature semiconducting systems such as self-assembled InGaAs quantum dots. In this work, we explore the emission properties of quantum emitters in a WSe2 monolayer which are induced by metallic nanoparticles. Under quasi-resonant pulsed excitation, we verify clean single-photon emission with a g((2))(0) = 0.036 +/- 0.004. Furthermore, we determine the temperature dependent coherence time via Michelson interferometry, where a value of (13.5 +/- 1.0) ps is extracted for the zero-phonon line at 4 K, which reduces to (9 +/- 2) ps at 8 K. Associated time-resolved photoluminescence experiments reveal a decrease of the decay time from (2.4 +/- 0.1) ns to (0.42 +/- 0.05) ns. This change in decay time is explained by a model which considers a F & ouml;rster-type resonant energy transfer process which yields a strong temperature induced energy loss from the single-photon emitters to the nearby Ag nanoparticle.