Revisiting lattice thermal conductivity of CsCl: The crucial role of quartic anharmonicity

Thermal conductivity ( κ L ) plays a critical role in thermal management applications. Usually, crystals with simpler structures exhibit higher κ L due to fewer phonon scatterings. However, cesium chloride (CsCl) presents an anomaly, demonstrating an unexpectedly low κ L of 1.0 W m⁻¹ K⁻¹ at 300 K, as observed in Professor Iversen's experimental measurement despite its simple structure. This prompts a need for understanding anomalous low κ L and matching theory with experimental observations. Our study brings forth several findings for CsCl: (i) relying solely on three-phonon scattering inadequately captures κ L . (ii) Anharmonic phonon renormalization significantly contributes to increased κ L . (iii) Coherent phonons align temperature-dependent κ L closely with the experiment. This work not only enhances understanding of anomalous κ L in CsCl but also provides an approach to bridge the gap between experiment and theory in other crystals.