Dark-exciton driven energy funneling into dielectric inhomogeneities in two-dimensional semiconductors

TL;DR

This study demonstrates that nanoscale dielectric inhomogeneities in 2D semiconductors can effectively funnel and trap dark excitons, enabling precise control of exciton transport through dielectric engineering.

Contribution

It reveals that dielectric nanobubbles can direct dark excitons in 2D TMDs, offering a new method for exciton transport control without significantly affecting bright exciton energies.

Findings

Dielectric nanobubbles efficiently funnel excitons at room temperature.

Dark excitons are primarily responsible for energy funneling.

Exciton transport can be tuned via dielectric inhomogeneities.

Abstract

The optoelectronic and transport properties of two-dimensional transition metal dichalcogenide semiconductors (2D TMDs) are highly susceptible to external perturbation, enabling precise tailoring of material function through post-synthetic modifications. Here we show that nanoscale inhomogeneities known as nanobubbles can be used for both strain and, less invasively, dielectric tuning of exciton transport in bilayer tungsten disulfide (WSe2). We use ultrasensitive spatiotemporally resolved optical scattering microscopy to directly image exciton transport, revealing that dielectric nanobubbles are surprisingly efficient at funneling and trapping excitons at room temperature, even though the energies of the bright excitons are negligibly affected. Our observations suggest that exciton funneling in dielectric inhomogeneities is driven by momentum-indirect (dark) excitons whose energies are more sensitive to dielectric perturbations than bright excitons. These results reveal a new pathway to control exciton transport in 2D semiconductors with exceptional spatial and energetic precision using dielectric engineering of dark state energetic landscapes.