title: Mechanical Weyl Modes in Topological Maxwell Lattices.
abstract: We show that two-dimensional mechanical lattices can generically display topologically protected bulk zero-energy phonon modes at isolated points in the Brillouin zone, analogs of massless fermion modes of Weyl semimetals. We focus on deformed square lattices as the simplest Maxwell lattices, characterized by equal numbers of constraints and degrees of freedom, with this property. The Weyl points appear at the origin of the Brillouin zone along directions with vanishing sound speed and move away to the zone edge (or return to the origin) where they annihilate. Our results suggest a design strategy for topological metamaterials with bulk low-frequency acoustic modes and elastic instabilities at a particular, tunable finite wave vector.
authors.affiliation: Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109, USA.
authors.forename: D Zeb
authors.initials: DZ
authors.lastname: Rocklin
authors.affiliation: Instituut-Lorentz, Universiteit Leiden, 2300 RA Leiden, The Netherlands.
authors.forename: Bryan Gin-Ge
authors.initials: BG
authors.lastname: Chen
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Falk
authors.affiliation: Instituut-Lorentz, Universiteit Leiden, 2300 RA Leiden, The Netherlands.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Vitelli
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Lubensky