Tunable band gaps and symmetry breaking in magnetomechanical metastructures inspired by multilayer two-dimensional materials

Abstract

In this Letter, we introduce a paradigm to realize magneto-mechanical metastructures inspired by multi-layer 2D materials, such as graphene bilayers. The metastructures are intended to capture two aspects of their nanoscale counterparts. One is the multi-layer geometry, which is implemented by stacking hexagonal lattice sheets. The other is the landscape of weak inter-layer forces, which is mimicked by the interactions between pairs of magnets located at corresponding lattice sites on adjacent layers. We illustrate the potential of this paradigm through a three-layer prototype. The two rigid outer lattices serve as control layers, while the thin inner layer is free to experience flexural motion under the confining action of the magnetic forces exchanged with the outer ones, thus behaving as a lattice on elastic foundation. The inner layer is free to rotate relatively to the others, giving rise to a rich spectrum of inter-layer interaction patterns. Our objective is to determine how the dynamical response can be tuned by changing the twist angle between the layers. Specifically, we demonstrate experimentally that switching between different stacking patterns has profound consequences on the phonon landscape, opening and closing bandgaps in different frequency regimes.

Topological phononic metamaterials

“…For instance, a mechanical analog of twisted bilayer graphene made of two vibrating plates was studied in [686] in the aim of find the magic angles for quasiflat bands of phonons (specifically, the flexural waves) with vanishing group velocity. Similar purposes were pursued in other studies in acoustic and mechanical systems [685,687,689]. Later, the topological properties of twisted bilayers of phononic systems were studied [688,690] focusing on the phononic band gaps emerging due to the twisting and interlayer couplings.…”

“…The rise of twistronics and twist-photonics [681][682][683][684] has inspired the lots of studies on twisted phononic bilayers recently [685][686][687][688][689][690][691]. The study of twisted phononic systems started from the analog with twisted bilayer graphene with an aim of tuning the phononic bands via the twisting degree of freedom.…”