weakly coupled) excitons simply follows the angular profile of the absorption spectra taken at $2$ eV, thus observed over the anticrossing region. Resonant SH spectroscopy of our system therefore confirms the presence of the chiralitonic states, with the valley contrast of WS$_2$ and the spin-locking property of the OSO plasmonic resonator being imprinted on these new eigenstates of the system.

Revealed by these resonant SH measurements, the spin-locking property of chiralitonic states incurs however different relaxation mechanisms through the dynamical evolution of the chiralitons. In particular, excitonic intervalley scattering can erase valley contrast in WS$_2$ at RT [@Jonker2016] -see below. In our configuration, this would transfer chiraliton population from one valley to the other, generating via optical spin-locking, a reverse flow, racemizing the chiraliton population. This picture however does not account for the possibility of more robust valley contrasts in strong coupling conditions, as recently reported with MoSe$_2$ in Fabry-Pérot cavities [@Tartakovskii2016]. The chiralitonic flow is measured by performing angle resolved polarized PL experiments, averaging the signal over the PL lifetime of ca. $200$ ps (see Supporting Information, Sec. D and E). For these experiments, the laser excitation energy is chosen at $1.96$ eV, slightly below the WS$_2$ band-gap. At 