Fig. 2
Strong coupling between cooperative excitons and the first-order Bragg mode. a Schematic diagram of the full sample structure, where on the topmost layer is the CsPbBr3 QDs thin film, and beneath it is a 16 pairs DBR grow on a silicon substrate. b SF emission of QDs thin film on silicon and reflectivity spectrum of the bare DBR measured at 10 K. c Angle-resolved measured PL spectra for the QDs thin film on DBR. The band of the cooperative excitons is split up by coupling to the first Bragg mode. The observed Rabi splitting energy is ~ 21.6 meV. d Calculated polaritonic density of states as a function of angle and wavelength. The yellow dashed lines in (c, d) are tracing the dispersion of the polariton modes. e The second-order derivative diagram for (c). f Angle-resolved reflectivity spectra for the bare DBR, the 1st Bragg mode is shown at 537 nm
