Optical seminar | 19 March 2021
Exciton-polaritons (polaritons herein) are bosonic quasiparticles with unique physical properties arising from strong coupling between excitons and confined photons. Since their first demonstration , exciton-polaritons became a convenient platform for studies of collective quantum effects such as Bose-Einstein condensation  and superfluidity . To date, the most striking effects were cleanly demonstrated in GaAs- based microcavities due to the very low defect densities in those MBE-grown structures. However, polaritons in GaAs quantum wells can only exist at cryogenic temperatures, which limits practical applications for future optoelectronics. Operation at room temperature can be achieved by utilizing the more stable excitons in monolayers of transition metal dichalcogenide crystals (TMDCs) . Polariton condensation and superfluidity in these materials can potentially allow dissipationless transport at room temperature and form the basis for future optoelectronic devices with ultra-low energy consumption.
In this talk, I will demonstrate methods we have developed to make high-quality all-dielectric optical microcavities operating in the strong coupling regime between the excitons in the TMDC WS2 and the cavity photons at room temperature. These include a novel large-scale passivation and protection method for the integration of monolayer WS2 into an all-dielectric environment .
Further, I will talk about our studies of room-temperature exciton polaritons in a such a high-Q microcavity that incorporates a trapping potential for exciton polaritons. Our observations show that both trapped and freely propagating WS2 polaritons experience reduced dielectric disorder and exhibit signatures of ballistic transport with enhanced coherence below the onset of bosonic condensation. These findings represent significant insight into the behaviour of room-temperature TMDC exciton polaritons in engineered potential landscapes.
 C. Weisbuch, M. Nishioka, A. Ishikawa, and Y. Arakawa, Observation of the coupled exciton-photon mode splitting in a semiconductor quantum microcavity, Phys. Rev. Lett. 69, 3314-3317 (1992).
 J. Kasprzak, M. Richard, S. Kundermann, A. Baas, P. Jeambrun J. M. J. Keeling, F. M. Marchetti, M. H. Szymańska, R. André, J. L. Staehli, V. Savona, P. B. Littlewood, B. Deveaud, and L. S. Dang, Bose-Einstein condensation of exciton polaritons, Nature 443, 409-414 (2006).
 A. Amo, J. Lefrére, S. Pigeon, C. Adrados, C. Ciuti, I. Carusotto, R. Houdré, E. Giacobino, and A. Bramati, Superfluidity of polaritons in semiconductor microcavities, Nat. Phys. 5, 805-810 (2009).
 C. Schneider, M. M. Glazov, T. Korn, S. Höfling, and B. Urbaszek, Two-dimensional semiconductors in the regime of strong light-matter coupling, Nat. Commun. 9, 2695 (2018).
 M. Wurdack, T. Yun, E. Estrecho, N. Syed, S. Bhattacharyya, M. Pieczarka, A. Zavabeti, S.-Y. Shen, B. Haas, J. Müller, M. N. Lockrey, Q. Bao, C. Schneider, Y. Lu, M. S. Fuhrer, A. G. Truscott, T. Daeneke, and E. A. Ostrovskaya, Adv. Mater. 33, 2005732 (2021).