Excitonic Mott insulator in a Bose-Fermi-Hubbard system of moiré WS₂/WSe₂ heterobilayer

Understanding the Hubbard model is crucial for investigating various quantum many-body states and its fermionic and bosonic versions have been largely realized separately. Recently, transition metal dichalcogenides heterobilayers have emerged as a promising platform for simulating the rich physics of the Hubbard model. In this work, we explore the interplay between fermionic and bosonic populations, using a WS₂/WSe₂ heterobilayer device that hosts this hybrid particle density. We independently tune the fermionic and bosonic populations by electronic doping and optical injection of electron-hole pairs, respectively. This enables us to form strongly interacting excitons that are manifested in a large energy gap in the photoluminescence spectrum. The incompressibility of excitons is further corroborated by observing a suppression of exciton diffusion with increasing pump intensity, as opposed to the expected behavior of a weakly interacting gas of bosons, suggesting the formation of a bosonic Mott insulator. We explain our observations using a two-band model including phase space filling. Our system provides a controllable approach to the exploration of quantum many-body effects in the generalized Bose-Fermi-Hubbard model.. Authors: Gao, Beini [University of Maryland, College Park, MD (United States). Joint Quantum Institute (JQI); OSTI] (ORCID:0000000245444962); Suárez-Forero, Daniel G. [University of Maryland, College Park, MD (United States). Joint Quantum Institute (JQI)] (ORCID:0000000227576320); Sarkar, Supratik [University of Maryland, College Park, MD (United States). Joint Quantum Institute (JQI)] (ORCID:0000000326452307); Huang, Tsung-Sheng [University of Maryland, College Park, MD (United States). Joint Quantum Institute (JQI)]; Session, Deric [University of Maryland, College Park, MD (United States). Joint Quantum Institute (JQI)]. DOE Contract: SC0022885. Subjects: 36 MATERIALS SCIENCE; Science & Technology - Other Topics