Enhancement of the lattice thermal conductivity of two-dimensional functionalized MXenes by inversion symmetry breaking

Crystal symmetry plays a critical role in thermal transport in solids. One example is mirror symmetry in monolayer graphene that promotes thermal transport by forbidding certain phonon scattering channels. Here, we show an interesting counterexample in monolayer ${\mathrm{Ta}}_{2}\mathrm{C}{\mathrm{S}}_{2}$ that inversion symmetry breaking can abnormally enhance lattice thermal conductivity of two-dimensional (2D) functionalized MXenes based on the phonon Boltzmann transport theory combined with first-principles calculations. We find inversion symmetry breaking not only affects scattering channels but also redistributes the charge and changes the anharmonic phonon properties. Both atomic vibrations in real space and phonon scattering rates in the reciprocal space confirm the significantly reduced lattice anharmonicity in an asymmetric ${\mathrm{Ta}}_{2}\mathrm{C}{\mathrm{S}}_{2}$ sheet, leading to substantially enhanced thermal conductivity after inversion symmetry breaking. The physical origin for the variation of anharmonic properties induced by symmetry is discussed in detail. In this paper, we provide insight into the complex role of symmetry on thermal transport in 2D functionalized MXenes.