Probing mesoscopic nonlocal screening in van der Waals heterostructures with polaritons

TL;DR

This study reveals a mesoscopic nonlocal screening effect in van der Waals heterostructures, extending up to 140 nm, which impacts optical modelling and device design by providing a transferable metric related to charge transfer.

Contribution

It uncovers a mesoscopic nonlocal screening regime in vdW heterostructures and introduces a transferable metric based on phonon polariton shifts for charge transfer.

Findings

Nonlocal screening extends up to ~140 nm at buried interfaces.

A thickness-independent saturated response is observed as MoO3 is thinned.

The charge transfer metric scales linearly with work-function difference.

Abstract

Predictive optical modelling of van der Waals (vdW) heterostructures is critical for meta-optics, near-field photonics and quantum technologies. At their buried interfaces, charge transfer and spatially extended screening challenge local descriptions based on layer-by-layer stacking of fixed permittivity tensors. However, such nonlocal corrections have been established mainly for plasmonic systems at {\aa}ngstr\"om-nanometre scales and are often assumed negligible on optical-wavelength scales. Here we challenge this view by uncovering a mesoscopic nonlocal screening regime, extending up to ~140 nm, at buried charge-transfer interfaces in transition-metal dichalcogenide/{\alpha}-molybdenum trioxide (TMDC/{\alpha}-MoO3) phonon-polaritonic heterostructures. Using phonon polaritons as an ultrasensitive probe, we quantify charge transfer from polariton-wavelength shifts and find a thickness-independent saturated response as {\alpha}-MoO3 is thinned. Rather than merely complicating optical modelling, this nonlocal saturation turns a design-level correction into an opportunity by yielding a transferable cross-material metric. Across more than 120 devices, this metric scales linearly with the work-function difference between the TMDC and {\alpha}-MoO3. We further identify a lattice-mismatch-set energy threshold for charge transfer, revising Anderson-type band alignment for vdW interfaces.