Anharmonicity driven unusual particle-to-wave-like phonon crossover leads to ultralow thermal conductivity in Tl2AgI3

Proceedings of the National Academy of Sciences, Volume 123, Issue 4, January 2026. <br/>SignificanceThermal transport in crystalline solids is typically governed by particle-like phonon propagation. Here, we find a rare and experimentally validated transition from particle-like propagation to wave-like coherence in the zero-dimensional (0D) …