Unusually high phonon thermal conductivity in the Weyl semimetal TaP: A comparative study with TaAs

In many metals, thermal transport is often dominated by electrons, although the lattice contribution can remain appreciable depending on the material. Here, through rigorous first-principles calculations, we uncover a phonon-dominated thermal transport regime in the Weyl semimetals TaAs and TaP. Remarkably, despite its metallic character, TaP exhibits an exceptionally high phonon thermal conductivity ($\kappa_{\text{ph}}$) of 162 Wm$^{-1}$K$^{-1}$ at room temperature, surpassing its electronic counterpart by nearly an order of magnitude. This anomalously high $\kappa_{\text{ph}}$ is enabled by the unique electronic and phononic band structures, including the Weyl nodes near the Fermi level, acoustic phonon bunching, and a wide frequency gap in the phonon spectrum, which collectively suppress phonon-electron and three-phonon scattering processes. The linearly dispersing bands near the Fermi level give rise to a low electronic density of states, thereby limiting both electrical conductivity and electronic thermal transport in these Weyl semimetals. By further surveying a broad range of topological semimetals, we show that the prominence of phonon thermal transport is a universal characteristic of this material class. Our work provides deeper insight into thermal transport mechanisms in topological semimetals and broadens the scope for discovering metals with high thermal conductivity.