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

Frisenda, Riccardo; Sanchez-Santolino, Gabriel; Papadopoulos, Nikos; Urban, Joanna; Baranowski, Michal; Surrente, Alessandro; Maude, Duncan K; Garcia-Hernandez, Mar et al. · Nano Lett · 2020

basic_science · Level V

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Abstract

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.