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Nontrivial strength of van der Waals epitaxial interaction in soft perovskites

The van der Waals (vdW) bond is traditionally believed to be orders of magnitude lower than the typical chemical bond (i.e., ionic, metallic, or covalent), and hence the effects caused by a vdW interface are thought to be trivial. In this paper, by investigating the vdW epitaxial growth of a mechanically soft perovskite on the vdW substrate, we obtained the solid proof of strong non-negligible vdW interaction. The experimental results illustrate the formation of cracks and holes for the relaxation of the vdW strain as well as a lattice-constant-dependent epitaxial angle evolution and a pronounced band-structure change. The first-principles calculations indicate that the contribution of the vdW interaction energy at the epitaxial interface reaches up to more than a quarter of the overall interaction energy far exceeding the traditionally recognized vdW bonding strength. Both the experimental and the theoretical work show that given the appropriate material system, the vdW interaction could be strong enough to significantly manipulate material properties.