  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.
