The interplay between crystal symmetry and electron-phonon coupling is crucial for understanding thermal transport in two-dimensional materials. Using first-principles calculations combined with Wannier interpolation and coupled electron-phonon Boltzmann transport theory, we investigate how inversion-symmetry breaking affects the electronic structure, phonon spectrum, and thermal conductivity of monolayer ${\mathrm{Ta}}_2{\mathrm{CS}}_2$. We find that the symmetric structure is metallic, whereas the asymmetric structure is semiconducting with a narrow band gap. In the symmetric structure, electrons contribute about 40% of the total thermal conductivity at 300 K. In contrast, in the asymmetric structure the electronic contribution becomes negligible, while electron-phonon coupling strongly suppresses phonon heat transport under carrier doping. At 300 K and a carrier concentration of ${10}^{14} {\mathrm{cm}}^{-2}$, the lattice thermal conductivity decreases from $103.5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ to 15.7 and $7.3\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ for hole and electron doping, respectively. Symmetry analysis indicates that inversion-symmetry breaking relaxes the selection rules and opens additional scattering channels, while the accompanying charge redistribution increases the electron-phonon matrix elements, together leading to enhanced phonon-electron scattering. Our results demonstrate that symmetry breaking can strongly modify electron-phonon coupling and the associated thermal transport, highlighting symmetry control as an effective strategy for tuning heat conduction in two-dimensional polar materials.

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• Electron thermal conductivity
• Lattice thermal conductivity
• 2-dimensional systems
• MXenes
• Boltzmann theory
• Density functional calculations
• First-principles calculations