Symmetry Breakdown in Franckeite: Spontaneous Strain, Rippling and Interlayer Moiré

13 August 2019, Version 1

Abstract

Franckeite is a naturally occurring layered mineral with a structure composed of alternating stacks of SnS2-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 SnS2-like and PbS-like lattices incommensurability.

Keywords

2D superlattice
van der Waals superlattice
franckeite
symmetry breakdown

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