High Degree Valley-Polarization from Interlayer Exciton in van der Waals Heterostructure

Two-dimensional semiconductors promise valleytronics applications, where the valleys of the electronic bands, in addition to spin and charge, become a new degree of freedom for quantum engineering and information processing. Yet electron-hole exchange interactions lead to rapid valley depolarization and low valley polarizations (VPs) in monolayer materials. Here, by precisely aligning the momentum valleys of a WSe₂ monolayer to a MoSe₂ monolayer, we form a hetero-bilayer with bright interlayer excitons that inherit and preserve the VP from the intralayer ones while at the same time with greatly suppressed electron-hole exchange interactions. Using these hetero-bilayers, We demonstrate brightened spin triplet inter-layer excitons localized at the potential minimum of the moiré lattice with a VP up to 80% and a valley lifetime of 33 ns. Spin singlet transition localized at the same registry is also measured, with an as high but opposite VP. Our work leads the way of using van der Waals semiconductor heterostructures to control the charge transfer, VP, optical selection rules and other novel optoelectronic properties.