  Since dissipative processes are ubiquitous in semiconductors, characterizing
how electronic and thermal energy transduce and transport at the nanoscale is
vital for understanding and leveraging their fundamental properties. For
example, in low-dimensional transition metal dichalcogenides (TMDCs), excess
heat generation upon photoexcitation is difficult to avoid since even with
modest injected exciton densities, exciton-exciton annihilation still occurs.
Both heat and photoexcited electronic species imprint transient changes in the
optical response of a semiconductor, yet the unique signatures of each are
difficult to disentangle in typical spectra due to overlapping resonances. In
response, we employ stroboscopic optical scattering microscopy (stroboSCAT) to
simultaneously map both heat and exciton populations in few-layer \ch{MoS2} on
relevant nanometer and picosecond length- and time scales and with 100-mK
temperature sensitivity. We discern excitonic contributions to the signal from
heat by combining observations close to and far from exciton resonances,
characterizing photoinduced dynamics for each. Our approach is general and can
be applied to any electronic material, including thermoelectrics, where heat
and electronic observables spatially interplay, and lays the groundwork for
direct and quantitative discernment of different types of coexisting energy
without recourse to complex models or underlying assumptions.
