  The interplay of optics, dynamics and transport is crucial for the design of
novel optoelectronic devices, such as photodetectors and solar cells. In this
context, transition metal dichalcogenides (TMDs) have received much attention.
Here, strongly bound excitons dominate optical excitation, carrier dynamics and
diffusion processes. While the first two have been intensively studied, there
is a lack of fundamental understanding of non-equilibrium phenomena associated
with exciton transport that is of central importance e.g. for high efficiency
light harvesting. In this work, we provide microscopic insights into the
interplay of exciton propagation and many-particle interactions in TMDs. Based
on a fully quantum mechanical approach and in excellent agreement with
photoluminescence measurements, we show that Auger recombination and emission
of hot phonons act as a heating mechanism giving rise to strong spatial
gradients in excitonic temperature. The resulting thermal drift leads to an
unconventional exciton diffusion characterized by spatial exciton halos.
