Semiconducting monolayers and the prospect of valley-polaritonics || Roel Tempelaar

Inversion symmetry breaking in hexagonal atomic monolayers results in two inequivalent K points in the Brillouin zone. Monolayer transition-metal dichalcogenides (TMDs) are semiconductors with an optical gap located inside the band valleys around such inequivalent K points. Combined with strong spin-orbit coupling, this gives rise to a conserved valley pseudospin that can be directly coupled to with circularly-polarized light. In this talk, I will discuss our recent eort to theoretically understand the polariton states emerging in optically-confined TMDs in terms of their valley-composition and circular polarization. Our calculations demonstrate that polariton formation can open a new relaxation pathway for the valley pseudospin, which is facilitated by the degeneracy of the two inequivalent valleys. Interestingly, our results suggest that a confinement under chiral optical fields will lift this valley degeneracy, yielding polariton states with a conserved valley pseudospin. This not only opens the possibility to engineer valley-polaritonics, but to also spectrally shift the polariton states depending on their valley-composition, by means of a polariton-induced chiral Stark effect.