Low in-plane thermal conductivity in transition-metal dichalcogenides heterostructure originating from mirror symmetry breaking

The symmetry of a crystal structure is a pivotal factor in governing phonon heat transport. Heterostructures of low-dimensional materials provide a natural platform to control symmetry. To show that the lattice thermal conductivity can be modulated by heterostructures rather than a trivial average between their constituent materials, we employed the Boltzmann transport equation with the first-principles calculations to investigate the lattice thermal conductivity (κL) of the mirror symmetry breaking WS2/CrS2 heterostructure compared with the bilayer CrS2 and WS2. In contrast to common intuition, we found that the κL of the heterostructure is approximately four times lower than those of the bilayer WS2 and CrS2. To elucidate the underlying mechanisms, we analyzed the κL and the scattering rates of the acoustic and quasi-acoustic interlayer shear modes. Remarkably, the absence of mirror symmetry leads to unusually high scattering rates, significantly reducing their contribution to the total κL. Furthermore, this effect is further assessed by analyzing the relative vibrations of the atoms between layers. Our work offers insights into regulating thermal conductivity via symmetry engineering and suggests novel strategies for thermal management in future devices.