Identification of\nTwo-Dimensional Interlayer Excitons\nand Their Valley Polarization in MoSe<sub>2</sub>/WSe<sub>2</sub> Heterostructure\nwith <i>h</i>‑BN Spacer Layer

Interlayer excitons (IXs) in the heterostructure of monolayer\ntransition\nmetal dichalcogenides (TMDs) are considered as a promising platform\nto study fundamental exciton physics and for potential applications\nof next generation optoelectronic devices. The IXs trapped in the\nmoiré potential in a twisted monolayer TMD heterostructure\nsuch as MoSe<sub>2</sub>/WSe<sub>2</sub> form zero-dimensional (0D)\nmoiré excitons. Introducing an atomically thin insulating layer\nbetween TMD monolayers in a twisted heterostructure would modulate\nthe moiré potential landscape, thereby tuning 0D IXs into 2D\nIXs. However, the optical characteristics of IXs have not been elucidated.\nHere, we have experimentally investigated the significant optical\ncharacteristics arising from IXs in a MoSe<sub>2</sub>/<i>h</i>-BN/WSe<sub>2</sub> heterostructure by optical spectroscopy. The\nexperimental results of time-resolved photoluminescence spectroscopy\ncombined with phenomenological rate equation analysis reveal that\nthe radiative decay rate of IXs in the MoSe<sub>2</sub>/<i>h</i>-BN/WSe<sub>2</sub> heterostructure changes as a function of temperature,\nwhich strongly suggests the emergence of 2D IXs by the modulation\nof potential. Moreover, we demonstrate the valley polarization arising\nfrom the prolonged valley relaxation lifetime of 2D IXs reaching 100\nns at low temperature, which is dominated by electron–hole\nexchange interactions. These findings provide us with an effective\nstrategy to tailor the dimensionality of IXs and elucidate the desired\noptoelectronic response of IXs in monolayer semiconductor heterostructures.