Janus transition-metal dichalcogenide monolayers are fully artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>15 meV) spectra obfuscating their excitonic origin. Here, we identify the neutral, and negatively charged inter- and intravalley exciton transitions in Janus WSeS monolayer with ∼6 meV optical linewidth. We combine a recently developed synthesis technique, with the integration of Janus monolayers into vertical heterostructures, allowing doping control. Further, magneto-optic measurements indicate that monolayer WSeS has a direct bandgap at the K points. This work provides the foundation for applications such as nanoscale sensing, which relies on resolving excitonic energy shifts, and photo-voltaic energy harvesting, which requires efficient creation of long-lived excitons and integration into vertical heterostructures.
@article{arxiv.2210.06930,
title = {Identification of exciton complexes in a charge-tuneable Janus WSeS monolayer},
author = {Matthew S. G. Feuer and Alejandro R. -P. Montblanch and Mohammed Sayyad and Carola M. Purser and Ying Qin and Evgeny M. Alexeev and Alisson R. Cadore and Barbara L. T. Rosa and James Kerfoot and Elaheh Mostaani and Radosław Kalęba and Pranvera Kolari and Jan Kopaczek and Kenji Watanabe and Takashi Taniguchi and Andrea C. Ferrari and Dhiren M. Kara and Sefaattin Tongay and Mete Atatüre},
journal= {arXiv preprint arXiv:2210.06930},
year = {2022}
}