Artificial Thermal Anisotropy of Van der Waals Heterostructures

Van der Waals (vdW) heterostructures are rapidly emerging as a central focus of material research, where novel properties and unique functionalities can be created by stacking atomically thin layers with selected materials and sequence. Owing to highly anisotropic crystal structures, vdW heterostructures open up new avenues to develop artificial thermal anisotropy that is of both fundamental and practical importance. Here we provide a principle for the design of thermal anisotropy using vdW heterostructures based on mass ratio. Our first-principles calculations indicate that the increase of mass difference between neighbouring layers changes the shape of nonspherical isoenergy surfaces, resulting in enhanced thermal anisotropy. Meanwhile, ultralow cross-plane thermal conductivity can be achieved combined with phonon zone folding while high in-plane thermal conductivity can be preserved by considering phonon scattering channels. The present results demonstrate how novel materials that do not occur naturally can be created using vdW heterostructures.