# Symmetry breakdown in franckeite: spontaneous strain, rippling and interlayer moir\'e

## TL;DR

This study reveals that franckeite's layered structure spontaneously ripples and becomes anisotropic due to incommensurate lattice interactions, affecting its electrical, vibrational, and optical properties.

## Contribution

It uncovers the mechanism of symmetry breakdown in franckeite caused by interlayer lattice incommensurability and van der Waals interaction modulation.

## Key findings

- Spontaneous rippling induces structural anisotropy.
- Inhomogeneous in-plane strain correlates with rippling.
- Anisotropic electrical, vibrational, and optical responses observed.

## 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.

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Source: https://tomesphere.com/paper/1908.03922