<p>Franckeite is a naturally occurring layered mineral with a structure
composed of alternating stacks of SnS<sub>2</sub>-like and PbS-like layers. Although
this superlattice is composed of a sequence of isotropic two-dimensional
layers, it exhibits a spontaneous rippling that makes the material structurally
anisotropic. We demonstrate that this rippling comes hand in hand with an
inhomogeneous in-plane strain profile and anisotropic electrical, vibrational
and optical properties. We argue that this symmetry breakdown results from a
spatial modulation of the van der Waals interaction between layers due to the
SnS<sub>2</sub>-like and PbS-like lattices incommensurability.</p>
Influence of Pore Size on the van der Waals Interaction in Two-Dimensional Molecules and Materials
