Strong light-matter coupling: from traditional to cavity-free polaritons

Licentiate thesis, 2021

Polaritons are formed when light and matter interact strongly. For this to occur, photons and transitions in a material must exchange energy faster than the dissipation rate of the interacting components. Polaritons have shown the ability to change such material properties as photophysics, chemical reaction rates, transport, etc. Most of the studies on strong coupling use an external cavity. These sort of platforms form what here are called traditional polaritons. Moreover, such a cavity is often made of two metallic mirrors, which restrict access to the material.

The first part of the thesis is devoted to traditional polaritons in a microcavity-plasmon coupling platform. The versatility of the platform allows to achieve strong and ultrastrong coupling at room temperature. The second part is dedicated to cavity-free or self-hybridized polaritons. Here it is shown that polaritons can be sustained by the material with the transition resonance itself, by reshaping it into simple structures as slabs, cylinders, and spheres. The structures reveal a minimal critical size for polaritons to exist. Moreover, the coupling strength seems to be limited only by the macroscopic optical properties of the material.

These results can guide the community to quickly realize which materials can be used to form polaritons and to find them in simpler structures. Since the structures are not restricted by an external cavity, a window of opportunity is open for applications and further studies on the impact of polaritons on material properties.