Giant enhancement of exciton diffusion near an electronic Mott insulator

Bose-Fermi mixtures naturally appear in various physical systems. In
semiconductor heterostructures, such mixtures can be realized, with bosons
as excitons and fermions as dopant charges. However, the complexity of
these hybrid systems challenges the comprehension of the mechanisms that
determine physical properties such as mobility. In this study, we
investigate interlayer exciton diffusion in an H-stacked WSe2/WS2
heterobilayer. Our measurements are performed in the dilute exciton
density limit at low temperatures to examine how the presence of charges
affects exciton mobility. Remarkably, for charge doping near the Mott
insulator phase, we observe a giant enhancement of exciton diffusion of
three orders of magnitude compared to charge neutrality. We attribute this
observation to mobile valence holes, which experience a suppressed moire
potential due to the electronic charge order in the conduction band, and
recombine with any conduction electron in a non-monogamous manner. This
new mechanism emerges for sufficiently large fillings in the vicinity of
correlated generalized Wigner crystal and Mott insulating states. Our
results demonstrate the potential to characterize correlated electron
states through exciton diffusion and provide insights into the rich
interplay of bosons and fermions in semiconductor heterostructures.