Anisotropic Excitons and Polaritons

Anisotropy is a fundamental property of materials widely exploited in science and engineering. However, the interplay between the material and engineered photonic anisotropies has been difficult to access. Van der Waals materials open the opportunity to explore a wide range of anisotropic materials and to integrate them with photonic structures. We show here a matter-light hybrid system, exciton-polaritons in a 2D antiferromagnet, CrSBr, coupled with an anisotropic photonic crystal cavity, where the spin, atomic lattice, and photonic lattices anisotropies intertwine and give rise to unusual properties of the hybrid system. We measure strong coupling between engineered anisotropic optical modes and anisotropic excitons in CrSBr, which is stable against excitation densities a few orders of magnitude higher than polaritons in isotropic materials. Moreover, the polaritons feature a highly anisotropic polarization tunable by tens of degrees by controlling the matter-light coupling via, for instance, spatial alignment between the material and photonic lattices, magnetic field, temperature, cavity detuning and cavity quality-factors.