Excitons and trions in WSSe monolayers

TL;DR

This study investigates the optical properties of WSSe monolayers, revealing excitons, trions, and single photon emitters, with implications for quantum technologies and tunable 2D materials.

Contribution

It provides the first detailed analysis of excitonic and trionic states in WSSe monolayers, including magnetic field effects and single photon emission capabilities.

Findings

Identification of neutral bright A exciton in WSSe MLs

Observation of negatively charged excitons (trions)

Detection of single photon emitters in WSSe MLs

Abstract

The possibility of almost linear tuning of the band gap and of the electrical and optical properties in monolayers (MLs) of semiconducting transition metal dichalcogenide (S-TMD) alloys opens up the way to fabricate materials with on-demand characteristics. By making use of photoluminescence spectroscopy, we investigate optical properties of WSSe MLs with a S/Se ratio of 57/43 deposited on SiO$_2$/Si substrate and encapsulated in hexagonal BN flakes. Similarly to the $"parent"$ WS$_2$ and WSe$_2$ MLs, we assign the WSSe MLs to the ML family with the dark ground exciton state. We find that, in addition to the neutral bright A exciton line, three observed emission lines are associated with negatively charged excitons. The application of in-plane and out-of-plane magnetic fields allows us to assign undeniably the bright and dark (spin- and momentum-forbidden) negative trions as well as the phonon replica of the dark spin-forbidden complex. Furthermore, the existence of the single photon emitters in the WSSe ML is also demonstrated, thus prompting the opportunity to enlarge the wavelength range for potential future quantum applications of S-TMDs.