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.

[@skinwalker9878]

So confused on the concept of pseudospin...So if only RCP(LCP) populates K(K') valley as "real" spins and and valleys are coupled. What are the roles of valley pseudospins? I get that they make the K & K' valleys distinct due to the order of the pseudospins, but how can RCP(LCP) excite both "up" and "down" pseudospins in the specific valleys?

[@Toro00_g9]

This seminar is really helpful for my next week presentation. Thank you sir,