Diverse Excitonic\nPhenomena in Asymmetric Trilayer\nTransition Metal Dichalcogenide Heterostructures

Interlayer excitons formed in two-dimensional\ntransition metal\ndichalcogenide (TMD) heterostructures can be easily tuned due to the\nlarge spatial separation. In this work, we discuss the electronic\nand excitonic optical properties of trilayer heterostructures MoS<sub>2</sub>/MoSSe/WSe<sub>2</sub> and MoS<sub>2</sub>/MoSSe/MoSe<sub>2</sub> using state-of-the-art <i>GW</i>+BSE calculations.\nIn both trilayer geometries, we discover a variety of exciton states,\nincluding interlayer excitons, every-other-layer excitons, and their\nhybridized states, <i>h</i>-IX. Importantly, the <i>h</i>-IXs are optically bright through hybridizing with the\nintralayer excitons, and the radiative lifetimes of <i>h</i>-IXs range from subnanoseconds to tens of microseconds at 77 K, depending\non their compositions. We also reveal that the diversity of the low-lying\nIXs in MoS<sub>2</sub>/MoSSe/MoSe<sub>2</sub> is higher than that\nof MoS<sub>2</sub>/MoSSe/WSe<sub>2</sub>, because more energy levels\nparticipate in transitions in MoS<sub>2</sub>/MoSSe/MoSe<sub>2</sub>. Our findings demonstrate that the appropriate energy alignment\nvia manipulating the Janus layer is crucial for realizing rich excitonic\nstates in trilayer TMD heterostructures.