# Highly Valley-Polarized Singlet and Triplet Interlayer Excitons in van der Waals Heterostructure

## TL;DR

This paper demonstrates highly valley-polarized interlayer excitons in van der Waals heterostructures, revealing mechanisms for prolonged valley polarization and potential for valleytronic device applications.

## Contribution

It reports the first observation of singlet and triplet interlayer excitons with over 80% valley polarization in WSe2/MoSe2 heterobilayers, clarifying valley depolarization mechanisms.

## Key findings

- Over 80% valley polarization in interlayer excitons
- Identification of direct band-gap exciton transition
- Ultrafast charge separation and suppressed valley depolarization

## Abstract

Two-dimensional semiconductors feature valleytronics phenomena due to locking of the spin and momentum valley of the electrons. However, the valley polarization is intrinsically limited in monolayer crystals by the fast intervalley electron-hole exchange. Hetero-bilayer crystals have been shown to have a longer exciton lifetime and valley depolarization time. But the reported valley polarization was low; the valley selection rules and mechanisms of valley depolarization remains controversial. Here, we report singlet and brightened triplet interlayer excitons both with over 80% valley polarizations, cross- and co-polarized with the pump laser, respectively. This is achieved in WSe2/MoSe2 hetero-bilayers with precise momentum valley alignment and narrow emission linewidth. The high valley polarizations allow us to identify the band minima in a hetero-structure and con_rm unambiguously the direct band-gap exciton transition, ultrafast charge separation, strongly suppressed valley depolarization. Our results pave the way for using semiconductor heterobilayers to control valley selection rules for valleytronic applications.