Four-phonon and electron-phonon scattering effects on thermal properties in two-dimensional 2H-TaS₂

Thermal transport characteristics of monolayer trigonal prismatic tantalum disulfide (2H-TaS₂) are investigated using first-principles calculations combined with the Boltzmann transport equation. Due to a large acoustic-optical phonon gap of 1.85 THz, the four-phonon (4ph) scattering significantly reduces the room-temperature phononic thermal conductivity (κ_ph). With the further inclusion of phonon-electron scattering, κ_ph reduces to 1.78 W mK⁻¹. Nevertheless, the total thermal conductivity (κ_total) of 7.82 W mK⁻¹ is dominated by the electronic thermal conductivity (κ_e) of 6.04 W mK⁻¹. Due to the electron-phonon coupling, κ_e differs from the typical estimation based on the Wiedemann-Franz law with a constant Sommerfeld value. This work provides new insights into the physical mechanisms for thermal transport in metallic 2D systems with strong anharmonic and electron-phonon coupling effects. The phonon scattering beyond three-phonon (3ph) scattering and even κ_e are typically overlooked in computations, and the constant Sommerfeld value is widely used for separating κ_e and κ_ph from the experimental thermal conductivity. These conclusions have implications for both the computational and experimental measurements of the thermal properties of transition metal dichalcogenides.