Condensation of exciton polaritons in a flatband of a deformed triangle lattice at room temperature

Flatbands in the periodic electronic or photonic structures attract intensive attention due to their infinite effective mass, which leads to plenty of physical phenomena, for example, the localization of electrons or photons. However, direct observation of bosonic condensate in the triangle lattice with tunable flatband at room temperature is not realized yet. In this work, we fabricated a microcavity with a triangle lattice potential and perovskite CsPbBr₃ as the gain material at room temperature. In this microcavity, polariton bands due to the coupling among the triangle lattice are observed, and exciton polariton condensation is realized. By deforming the triangle lattice such that the coupling between the potential sites is modulated, two exciton polariton flatbands with different energies are observed. Above threshold, exciton polaritons condense at the higher-energy flatband, which experiences larger gain. Our results offer a method to investigate the polariton flatband induced interesting physical phenomenon by engineering a two-dimensional photonic lattice at room temperature.