Resolving spin, valley, and moir\'e quasi-angular momentum of interlayer excitons in WSe2/WS2 heterostructures

TL;DR

This paper reports the observation and characterization of interlayer excitons in WSe2/WS2 heterostructures, revealing how moiré superlattices influence their spin, valley, and quasi-angular momentum, with implications for optoelectronic applications.

Contribution

It provides the first unambiguous determination of the spin, valley, and moiré quasi-angular momentum of interlayer excitons in moiré superlattices using novel spectroscopic techniques.

Findings

Multiple interlayer exciton states coexist in the heterostructure.

Interlayer excitons at different moiré sites exhibit opposite optical selection rules.

Moiré quasi-angular momentum influences exciton localization and optical properties.

Abstract

Moir\'e superlattices provide a powerful way to engineer properties of electrons and excitons in two-dimensional van der Waals heterostructures. The moir\'e effect can be especially strong for interlayer excitons, where electrons and holes reside in different layers and can be addressed separately. In particular, it was recently proposed that the moir\'e superlattice potential not only localizes interlayer exciton states at different superlattice positions, but also hosts an emerging moir\'e quasi-angular momentum (QAM) that periodically switches the optical selection rules for interlayer excitons at different moir\'e sites. Here we report the observation of multiple interlayer exciton states coexisting in a WSe2/WS2 moir\'e superlattice and unambiguously determine their spin, valley, and moir\'e QAM through novel resonant optical pump-probe spectroscopy and photoluminescence excitation spectroscopy. We demonstrate that interlayer excitons localized at different moir\'e sites can exhibit opposite optical selection rules due to the spatially-varying moir\'e QAM. Our observation reveals new opportunities to engineer interlayer exciton states and valley physics with moir\'e superlattices for optoelectronic and valleytronic applications.