Revisiting phonon thermal transport in perovskite CsPbBr3 crystals: Critical role of temperature-dependent quartic anharmonicity

Understanding the origin of ultralow lattice thermal conductivity (κL) in crystals is crucial for the development of advanced thermoelectric and thermal management materials. This study systematically investigates thermal transport mechanisms in perovskite CsPbBr3 crystals using a novel framework that integrates quartic anharmonicity-driven phonon spectral renormalization at finite temperatures with machine learning potential-driven molecular dynamics. In contrast to results from ground-state anharmonic lattice dynamics, our findings reveal that the ultralow κL in CsPbBr3 predominantly arises from particle-like phonon propagation rather than wave-like phonon coherence, due to anharmonic renormalization shifting most phonon modes from the Wigner limit into the propagation regime. Furthermore, the temperature-dependent quartic anharmonicity effectively promotes particle-like while limiting wave-like phonon transport channels, accurately reproducing the experimental ultralow κL of CsPbBr3 in magnitude and temperature dependence. This study not only resolves the discrepancy between measured and predicted κL in CsPbBr3 crystals but also reveals the dominant role of particle-like phonon propagation in flat ultralow κL, providing a revised physical picture for understanding anharmonic thermal transport and critical insights for regulating κL of materials through lattice anharmonicity.