Charge-density wave-mediated soft phonon modes suppress the temperature dependence of lattice thermal conductivity in 2H-NbSe2

Layered NbSe2 has attracted extensive interest as a prototypical system where multiband superconductivity coexists with a charge-density wave (CDW) order. Here, using self-consistent phonon theory to incorporate anharmonic renormalization, CDW critical temperatures in the bulk and monolayer 2H-NbSe2 are calculated to be 66 and 116 K, respectively, in good agreement with reported experiments. First-principles anharmonic lattice dynamics combined with Peierls–Boltzmann transport theory reveals that strong phonon anharmonicity, arising from low-energy special soft phonon modes mediated by the CDW behavior, results in a low lattice thermal conductivity (κL) with weak temperature dependence. Strikingly, four-phonon (4ph) interactions contribute to a dramatic suppression of κL, particularly in the in-plane direction, reinforcing the critical role of strong phonon anharmonicity. These results provide a detailed microscopic understanding of CDW transition and thermal transport in CDW materials.