Valley-Polarized Interlayer Excitons in 2D Chalcogenide-Halide Perovskite-van der Waals Heterostructures

Interlayer excitons (IXs) in two-dimensional (2D) heterostructures provide an exciting avenue for exploring optoelectronic and valleytronic phenomena. Presently, valley-tronic research is limited to transition metal dichalcogenide (TMD) based 2D heterostructure samples, which require strict lattice (mis) match and interlayer twist angle requirements. Here, we explore a 2D heterostructure system with exper-imental observation of spin-valley layer coupling to realize helicity-resolved IXs, without the requirement of a specific geometric arrangement, i.e., twist angle or specific thermal annealing treatment of the samples in 2D Ruddlesden-Popper (2DRP) halide perovskite/2D TMD heterostructures. Using first-principle calculations, time-resolved and circularly polarized luminescence measurements, we demonstrate that Rashba spin-splitting in 2D perovskites and strongly coupled spin-valley physics in monolayer TMDs render spin-valley-dependent optical selection rules to the IXs. Consequently, a robust valley polarization of similar to 14% with a long exciton lifetime of similar to 22 ns is obtained in type-II band aligned 2DRP/TMD heterostructure at similar to 1.54 eV measured at 80 K. Our work expands the scope for studying spin-valley physics in heterostructures of disparate classes of 2D semiconductors.

Automated summary

This article investigates the interlayer exciton phenomenon in two-dimensional heterostructures, and demonstrates the observation of helicity-resolved interlayer excitons through spin-valley layer coupling. This method does not require a specific geometric arrangement, such as twist angle or thermal annealing. The research shows that there are spin-valley-dependent optical selection rules in two-dimensional perovskites and monolayer transition metal dichalcogenides.