A new perspective in understanding the room-temperature superfluorescence from perovskites: collectively coherent excitonic polaron state

Albeit that there appeared sporadic reports of high-temperature superfluorescence (SF) (especially room-temperature SF) from metal-halide perovskites in the last decade, the mechanism of how coherent macroscopic quantum state resisted thermal dephasing effect was elusive. However, in the recent work published in Nature, Gundogdu et al. provided compelling evidence to show that beyond a critical polaron density, the incoherent disordered polaronic lattice deformations in a quasi-2D lead-halide perovskite PEA:CsPbBr₃ thin film established an order through thermal lattice vibration at room temperature, and the collectively coherent excitonic polaron state (soliton) emerged simultaneously. Particularly, during the process of phase correlation, the rocking vibration mode of polaron responded anharmonically to the stretching mode, which subsequently created an impedance for the stretching mode and ultimately suppressed the detrimental stretching oscillation that would cause dephasing. These results are unprecedented and their research provides new physical insights into macroscopic quantum coherence, and also will help researchers to unravel the origin of high-temperature SF recently reported in quantum dot superlattice systems.