State- and momentum-dependent nonlinear Stark effect of interlayer excitons in bilayer WSe$_2$

TL;DR

This paper investigates how interlayer excitons in bilayer WSe$_2$ respond to external electric fields, revealing a nonlinear Stark effect influenced by layer localization and hybridization, with implications for optoelectronic applications.

Contribution

It demonstrates the layer-dependent nonlinear Stark shift of interlayer excitons in bilayer WSe$_2$ using Many-Body Perturbation Theory, linking exciton response to layer hybridization.

Findings

Interlayer excitons exhibit a nonlinear Stark shift that becomes linear after a threshold.

Intralayer excitons are unaffected by external electric fields.

The nonlinearity degree correlates with layer hybridization of exciton components.

Abstract

Interlayer excitons in van der Waals heterostructures offer rich collective phases, prospective optoelectronic applications, and versatile tunability, where control by electronic means is particularly relevant and practical. Here, in the case of bilayer WSe$_2$, we reveal how layer localization of excitons governs their response to an external electric field. Using Many-Body Perturbation Theory, we calculate the exciton dispersion for different stacking symmetries under applied electric field and/or strain, in order to map the landscape of competing low-energy excitons in four distinct finite-momentum valleys. While intralayer excitons are not affected by the electric field, some interlayer ones exhibit a nonlinear Stark shift that becomes linear after a critical threshold. The degree of nonlinearity is a direct measure of the layer hybridization of the electronic subcomponents of the exciton. Our findings explain the peculiar Stark-shift regimes observed in recent experiments, the nature of (anti)symmetric spectral shifts around zero field, and the sensitivity of dipolar excitons to external perturbations, all highly relevant to their further applications in excitonic condensates, optoelectronics devices and quantum emitters.