Designing Quasi-Particles of light and Photon-Mediated Many-Body interactions in Cavity-Material Systems

Cavity material engineering is an innovative approach to material design which leverages spatially confined light to alter material properties. Light confined within a cavity serves as a gateway to creating light-matter hybrid states without requiring intense or damaging lasers. Remarkably, these hybrids can form even in dark cavities, due to the quantum nature of light, and they exhibit properties fundamentally different from their individual constituents, both at equilibrium and in excited states. Recent theoretical advancements predict cavity-modified material phases, including superconductivity, ferroelectricity, and magnetism [1]. Experimentally, pioneering studies are emerging: collective light-matter coupling has been proven to enhance ferromagnetism and induce metal-to-insulator transitions [2,3]. This talk will cover the advancements in the first-principles description of cavity-material systems, based on quantum electrodynamics (QED), with a focus on the emergence of novel light-matter hybrid states. Our atomistic framework demonstrates, among others, the formation of tunable novel quasiparticles of light, including 2D composite exciton-polariton states [4] which can display an all-optical Moiré confinement, and a three-way exciton-phonon-photon quasiparticle characterized by unique features in optical response [5]. It will further be shown that, under suitable assumptions, the light-matter problem can be reformulated as a pure matter problem, featuring a novel photon-induced electron-electron interaction. The impact of these emergent many-body interactions will be explored using QED Hartree-Fock to illustrate how strong light-matter interactions can lead to non-perturbative renormalization of material properties. Specifically, it will be shown that cavities can imprint spatial and time symmetries of light onto graphene's band structure [6]. This new theoretical framework enables simulations of light-matter coupled systems beyond the perturbative regime and provides the foundation to explore cavity-induced phenomena in a broader range of materials.