Strong matter-light coupling with novel materials

Supervisor: Dr Jonathan Keeling (St Andrews)

Polaritons are quasiparticles resulting from strong coupling between matter and light. Strong coupling occurs for photons confined in a microcavity, so that rather than photon emission being an irreversible loss process, photons that are emitted into the cavity can subsequently coherently excite the material again. This leads to new normal modes, polaritons. [1] Historically, much of the work on these quasiparticles made use of strong coupling to electronic excitations in inorganic semiconductors, such as GaAs or CdTe. However, recently there has been a lot of interest in polaritons formed from a wide variety of materials, including organic molecules (ranging from small molecules to organic polymer chains), as well as very recent developments for materials such as transition metal dichalcogenides, and hybrid organic-inorganic perovskits. These molecular systems have very strong matter-light coupling, and so the physics can be seen at room temperature. [1,2] One significant area of research concerns polariton condensation and lasing. Polaritons are bosons, and so Bose-Einstein condensation can be (and has been) seen. Because polaritons are part photon, they have a very low effective mass, leading to a very high transition temperature, indeed with organic materials, this can occur up to room temperature. Another area of increasing experimental interest is in using strong coupling to change material properties. In the context of organic molecules, this has included the idea of changing chemical reaction rates by strong coupling. This PhD position will be to explore theoretically models that capture the specific physics of a given material system, and ask how the physics of these materials affects, and is affected by, strong coupling to light. We will look both at the physics of Bose-Condensation, as well as modelling other possible applications of strong matter-light coupling to change material properties. We will make use of a variety of analytical and numerical techniques. For examples of our recent work see Refs. [3-5] [1] "The new era of polariton condensates." D. W. Snoke and J. Keeling Phys. Today 70 54 (2017) [2] "The road towards polaritonic devices." D. Sanvitto and S. Kéna-Cohen. Nat. Mater. 15 1061 (2016) [3] "Organic polariton lasing and the weak- to strong-coupling crossover" A. Strashko, P. Kirton, J. Keeling,Phys. Rev. Lett. 121 193601 (2018) [4] "Orientational alignment in cavity quantum electrodynamics." J. Keeling and P. G. Kirton. Phys. Rev. A 97 053836 (2018) [5] "Exact States and Spectra of Vibrationally Dressed Polaritons." M. A. Zeb, P. G. Kirton, and J. Keeling. ACS Photonics 5 249 (2018)