  Solid state cavity quantum electrodynamics is a rapidly advancing field which
explores the frontiers of light-matter coupling. Plasmonic approaches are of
particular interest in this field, since they carry the potential to squeeze
optical modes to spaces significantly below the diffraction limit1,2, enhancing
light-matter coupling. They further serve as an architecture to design
ultra-fast, non-linear integrated circuits with smallest footprints3.
Transition metal dichalcogenides are ideally suited as the active material in
such circuits as they interact strongly with light at the ultimate monolayer
limit4. Here, we implement a Tamm-plasmon-polariton structure, and study the
coupling to a monolayer of WSe2, hosting highly stable excitons5.
Exciton-Polariton formation at room temperature is manifested in the
characteristic energy-momentum dispersion relation studied in
photoluminescence, featuring an anti-crossing between the exciton and photon
modes with a Rabi-splitting of 23.5 meV. Creating polaritonic quasi-particles
in plasmonic architectures with atomic monolayers under ambient conditions is a
crucial step towards compact, highly non-linear integrated photonic and
polaritonic circuits6,7.
