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

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