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

Thermal conductivity (κL) plays a critical role in thermal management applications. Usually, crystals with simpler structures exhibit higher κL due to fewer phonon scatterings. However, cesium chloride (CsCl) presents an anomaly, demonstrating an unexpectedly low κL 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 κL and matching theory with experimental observations. Our study brings forth several findings for CsCl: (i) relying solely on three-phonon scattering inadequately captures κL. (ii) Anharmonic phonon renormalization significantly contributes to increased κL. (iii) Coherent phonons align temperature-dependent κL closely with the experiment. This work not only enhances understanding of anomalous κL in CsCl but also provides an approach to bridge the gap between experiment and theory in other crystals.