Identification of Exciton Complexes in Charge-Tunable Janus W<sub>Se</sub><sup>S</sup> Monolayers
Matthew S. G. Feuer, Alejandro R.‐P. Montblanch, Mohammed Sayyad, Carola M. Purser, Ying Qin, Evgeny M. Alexeev, Alisson R. Cadore, Bárbara L. T. Rosa, James Kerfoot, Elaheh Mostaani, Radosław Kalęba, Pranvera Kolari, Jan Kopaczek, Kenji Watanabe, Takashi Taniguchi, Andrea C. Ferrari, Dhiren M. Kara, Sefaattin Tongay, Mete Atatüre
Abstract
High Resolution Image Download MS PowerPoint Slide Janus transition-metal dichalcogenide monolayers are 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 (>18 meV) spectra obfuscating their specific excitonic origin. Here, we identify the neutral and the negatively charged inter- and intravalley exciton transitions in Janus W Se S monolayers with ∼6 meV optical line widths. We integrate Janus monolayers into vertical heterostructures, allowing doping control. Magneto-optic measurements indicate that monolayer W Se S has a direct bandgap at the K points. Our results pave the way for applications such as nanoscale sensing, which relies on resolving excitonic energy shifts, and the development of Janus-based optoelectronic devices, which requires charge-state control and integration into vertical heterostructures.