Fig. 1. 2D perovskite single crystal embedded in an optical cavity.

(A) Schematic representation of a 2D perovskite single crystal embedded in an optical cavity formed by two DBRs; in 2D perovskite, inorganic layers are separated by organic ligands realizing an effective multiple layered QW structure. (B) Energy versus in-plane momentum k photoluminescence emission from the sample represented in (A), with $k=\frac{2\mathrm{\pi }}{\mathrm{\lambda }}\text{sinθ}$, θ being the emission angle; the white dashed and solid lines represent the cavity and the exciton uncoupled modes, respectively, and the orange line is a fit to the polariton lower mode with E_X = 2.395 eV, E_C = 2.385 eV, and ℏΩ = 170 meV.