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 (κph). With the further inclusion of phonon-electron scattering, κph reduces to 1.78 W mK−1. Nevertheless, the total thermal conductivity (κtotal) of 7.82 W mK−1 is dominated by the electronic thermal conductivity (κe) of 6.04 W mK−1. Due to the electron-phonon coupling, κe 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 κe are typically overlooked in computations, and the constant Sommerfeld value is widely used for separating κe and κph from the experimental thermal conductivity. These conclusions have implications for both the computational and experimental measurements of the thermal properties of transition metal dichalcogenides.