The use of macroscopic coherent quantum states at room temperature is crucial in modern quantum technologies. In light of recent experiments demonstrating high-temperature superfluorescence in hybrid perovskite thin films, in this work we investigate the stability of the superradiant state concerning exciton-phonon interactions, taking into account the specifics of perovskites. We focused on quasi-two-dimensional (quasi-2D) Wannier excitons interacting with longitudinal optical (LO) phonons in polar crystals, as well as with acoustic phonons. Our study leads to the derivation of nonlinear equations in the coordinate space that govern the exciton wave function's coefficient in the single-exciton basis for the lowest exciton state, which translates to the complex-valued polarization. The resulting equations take the form of a 2D nonlocal nonlinear Schrodinger (NLS) equation. We perform a linear stability analysis of the plane wave solutions for the equations in question, which allows us to establish stability criteria. This analysis is particularly important for evaluating the stability of the superradiant state in the considered quasi-2D structures, as the superradiant state represents a specific case of the plane wave solution. Our findings indicate that, when the exciton interacts with LO phonons, a plane wave solution is modulationally stable, provided that the square of its amplitude does not exceed a critical intensity value defined by the exciton-LO phonon interaction parameters. In scenarios involving the weakly nonlocal NLS equation, we find that it transitions into a purely nonlocal form. The linear stability analysis yields results that align with those derived from the equation that does not consider weak nonlocality in the long-wave limit. Furthermore, interactions between the exciton and acoustic phonons reduce the intensity of modulationally stable waves compared to the case without such interactions. Our analytical results are corroborated by numerical calculations. We also numerically solve the 2D nonlocal NLS equation in polar coordinates and obtain its fundamental soliton solution, which is stable.

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• Excitons
• Light-matter interaction
• Luminescence
• Mesoscopics
• Optical & microwave phenomena
• Optical coherence
• Optical materials & elements
• Phonons
• Photonics
• Polarons
• Quantum coherence & coherence measures
• Quantum correlations, foundations & formalism
• Quantum interference effects
• Quantum optics
• Semiclassical physics
• Spontaneous emission