Polariton dispersion relations under condensation in a CuBr microcavity

We have investigated the exciton‐polariton condensation in a CuBr microcavity with HfO2/SiO2 distributed Bragg reflectors, focusing on condensation effects on polariton dispersion relations. The polariton distribution as a function of in‐plane wave vector k// under illumination was measured with angle‐resolved photoluminescence (PL) spectroscopy. In addition, we characterized the intrinsic polariton dispersion relations as reference data from analysis of the results obtained using angle‐resolved reflectance spectroscopy. It was found that the polariton condensation causes a large blueshift of the lower polariton branch (LPB) and a flat dispersion relation around the ground state at k//=0. The renormalized dispersion relation of the LPB under the polariton condensation was quantitatively analysed using a theory for a diffusive Goldstone mode peculiar to nonequilibrium condensation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)