Observation of Two Thresholds Leading to Polariton Condensation in 2D Hybrid Perovskites

2D perovskites are promising materials for photonic applications, given their outstanding nonlinear optical properties, ease of fabrication, and versatility. In particular, exploiting their high oscillator strength, the crystalline form of 2D perovskites can be used as excitonic medium in optical microcavities, allowing for the study of their optical properties in the strong light-matter coupling regime. While polariton condensation is observed in different materials at room temperature, for the first time two distinct threshold processes in a 2D perovskite are observed, a material that has never shown spontaneous phase transition up to now. In particular, lasing from the bi-exciton state is also demonstrated, which contributes to populate the lower polariton branch and, at higher excitation powers, eventually leads to the formation of a polariton condensate. The emission linewidth narrowing and a spatial coherence over 50 x 50 mu m(2) area is the smoking gun of a quantum coherent state formation in the 2D hybrid perovskite. The results not only show the formation of a polariton condensate in 2D perovskites but they are also crucial for the understanding of the physical mechanisms that lead to coherent phase transition in perovskite-based polariton microcavities.