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Anomalously High Phonon Thermal Conductivity Driven by Weak Electron-Phonon Coupling in Weyl Semimetals TaAs and TaP

In conventional metals, thermal transport is governed by electrons, with phonon contributions often considered negligible. Here, through rigorous first-principles calculations, we uncover a phonon-dominated thermal transport regime in the Weyl semimetals TaAs and TaP. Remarkably, although TaP is metallic, its phonon thermal conductivity ($κ_{\text{ph}}$) reaches as high as 171 Wm$^{-1}$K$^{-1}$ at room temperature, surpassing its electronic counterpart by more than a factor of five. This anomalously high $κ_{\text{ph}}$ is enabled by the unique electronic and phononic band structures, characterized by the Weyl nodes near the Fermi level, together with acoustic phonon bunching and a wide frequency gap in the phonon spectrum, which collectively suppress phonon-electron and phonon-phonon scattering processes. Due to the substantial phonon contribution, the derived Lorenz number deviates strongly from the conventional Wiedemann-Franz law. We further show that the significance of phonon thermal transport is universal across topological semimetals. Our work provides deeper insight into thermal transport mechanisms in topological semimetals and extends the scope for discovering materials with high thermal conductivity.