Fig. 1: Sketch of experimental configuration and characterizations of CsPbBr₃ microwire and plate.

a Schematics of polariton fluid experiments. The polariton fluid was resonantly pumped by a fs pulse laser, and the signal was detected in the transmission configuration (Supplementary Fig. 4). b, c are the optical images of a perovskite microwire and a plate under transmission configuration, respectively. Scale bar: 20 μm. d, e are the linear-polarized dispersions of photoluminescence (PL) of a perovskite microwire with a width of 1.85 μm and a plate along the two perpendicular crystal axes (x- and y-axis shown in Fig. b and c). Due to the confinement, the discrete energy levels along the y-axis of the microwire can be observed. Meanwhile, the spin-orbital coupling effect induces the two dispersion branches to cross along the y-axis. The dashed lines are the fittings of the two lower branches. The details of the fitting are shown in Supplementary Note 1. The two lower polariton branches with polarization along the x- (blue) and y- (red) axis cross at the diabolic points at k_y = 5.9 μm⁻¹.