Strain engineering of valley-polarized hybrid excitons in a 2D semiconductor

TL;DR

This paper reports the discovery of strain-tunable, valley-polarized hybrid excitons in monolayer TMDs, which combine properties of bright and dark excitons, offering enhanced polarization and slowed depolarization for valleytronic applications.

Contribution

It introduces a new class of strain-controlled hybrid excitons in 2D TMDs, demonstrating their enhanced polarization and coherence properties for quantum information technologies.

Findings

Hybrid excitons exhibit three times higher circular polarization.

Valley depolarization is slowed down a hundredfold.

Strain tuning enables control over valley polarization.

Abstract

Encoding and manipulating digital information in quantum degrees of freedom is one of the major challenges of today's science and technology. The valley indices of excitons in transition metal dichalcogenides (TMDs) are well-suited to address this challenge. Here, we demonstrate a new class of strain-tunable, valley-polarized hybrid excitons in monolayer TMDs, comprising a pair of energy-resonant intra- and intervalley excitons. These states combine the advantages of bright intravalley excitons, where the valley index directly couples to light polarization, and dark intervalley excitons, characterized by low depolarization rates. We demonstrate that the hybridized state of dark KK' intervalley and defect-localized excitons exhibits a degree of circular polarization of emitted photons that is three times higher than that of the constituent species. Moreover, a bright KK intravalley and a dark KQ exciton form a coherently coupled hybrid state under energetic resonance, with their valley depolarization dynamics slowed down a hundredfold. Overall, these valley-polarized hybrid excitons with strain-tunable valley character emerge as prime candidates for valleytronic applications in future quantum and information technology.