  The valley degree of freedom is one of the most intriguing properties of
atomically thin transition metal dichalcogenides. Together with the possibility
to address this degree of freedom by valley-contrasting optical selection
rules, it has the potential to enable a completely new class of future
electronic and optoelectronic devices. Resonant optical nanostructures emerge
as promising tools for interacting with and controlling the valley degree of
freedom at the nanoscale. However, a critical understanding gap remains in how
nanostructures and their nearfields affect the circular polarization properties
of valley-selective emission hindering further developments in this field. In
order to address this issue, our study delves into the experimental
investigation of a hybrid model system where valley-specific emission from a
monolayer of molybdenum disulfide is interacting with a resonant plasmonic
nanosphere. Contrary to the simple intuition suggesting that a centrosymmetric
nanoresonator preserves the degree of circular polarization in the forward
scattered farfield by angular momentum conservation, our cryogenic
photoluminescence microscopy reveals that the light emitted from the
nanoparticle position is largely unpolarized, i.e. we observe depolarization.
We rigorously study the nature of this phenomenon numerically considering the
monolayer-nanoparticle interaction at different levels including excitation and
emission. In doing so, we find that the farfield degree of polarization
strongly reduces in the hybrid system when including excitons emitting from
outside of the system's symmetry point, which in combination with
depolarisation at the excitation level causes the observed effect. Our results
highlight the importance of considering spatially distributed emitters for
precise predictions of polarization responses in these hybrid systems.
