Imaging Charged Exciton Localization in van der Waals\nWSe₂/MoSe₂ Heterobilayers

Abstract

Exciton\nlocalization in transition-metal dichalcogenide monolayers\nis behind a variety of interesting phenomena and applications, including\nbroad-spectrum solar cells and single-photon emissions. Strain fields\nat the periphery of topographically distinct features such as nanoscopic\nbubbles were recently associated with localized charge-neutral excitons.\nHere, we use tip-enhanced photoluminescence (PL) to visualize excitons\nin WSe₂/MoSe₂ heterobilayers (HBL). We find\nstrong optical emission from charged excitons, particularly positively\ncharged trions, in HBL supported by interlayer charge transfer. Our\nresults reveal strong trion confinement, with a localization length\nscale comparable to the trion size, at the apex region inside individual\nnanoscopic bubbles. Nano-PL mapping also shows sub-10-nm spatial variations\nin the localized trion emission spectra, which stem from atomic-scale\npotential energy fluctuations. These findings demonstrate the possibility\nof confining charged exciton complexes that are electrically tunable,\nopening up further opportunities to probe many-body exciton physics\nand to explore additional possible sites for strong exciton localization\nthat can lead to quantum emission.