Callaway's simplified heat flow model is often used to confirm experimental realizations of unconventional, hydrodynamic, and Poiseuille phonon transport in ultrahigh thermal conductivity $\left(\mathrm{<ruby><rb>\kappa </rb><rt>かっぱ</rt></ruby>}\right)$ materials, due to its simplicity and low computational cost. Here, we show that the Callaway model works exceptionally well for most ultrahigh-$\mathrm{<ruby><rb>\kappa </rb><rt>かっぱ</rt></ruby>}$ materials like diamond and boron nitride, but fails dramatically for boron arsenide (BAs) and boron antimonide (BSb). This failure is driven by the inability of the Callaway model to effectively describe the severely restricted phonon scattering in BAs and BSb, where many scattering selection rules are activated simultaneously. Our work highlights the powerful predictive capability of the Callaway model, and gives insights into the nature of phonon scattering in ultrahigh-$\mathrm{<ruby><rb>\kappa </rb><rt>かっぱ</rt></ruby>}$ materials and the suitability of Callaway's description of heat flow through them.

• Received 23 April 2023
• Revised 22 August 2023
• Accepted 21 September 2023

DOI:https://doi.org/10.1103/PhysRevB.108.155201