Amorphous topological insulators constructed from random point sets

• Published in: Nature physics Vol. 14; no. 4; pp. 380 - 385
• Main Authors: Mitchell, Noah P., Nash, Lisa M., Hexner, Daniel, Turner, Ari M., Irvine, William T. M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.04.2018; Nature Publishing Group
• Subjects: 639/766/119; 639/766/119/2792; 639/766/25; Atomic; Chirality; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Construction; Crystal structure; Crystallinity; Electronic systems; Gyroscopes; Lattices (mathematics); Letter; Mathematical and Computational Physics; Mathematical models; Metamaterials; Molecular; Optical and Plasma Physics; Periodic variations; Physics; Physics and Astronomy; Robustness (mathematics); Self-assembly; Theoretical; Topological insulators; Topology
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-017-0024-5

The discovery that the band structure of electronic insulators may be topologically non-trivial has revealed distinct phases of electronic matter with novel properties 1 , 2 . Recently, mechanical lattices have been found to have similarly rich structure in their phononic excitations 3 , 4 , giving rise to protected unidirectional edge modes 5 – 7 . In all of these cases, however, as well as in other topological metamaterials 3 , 8 , the underlying structure was finely tuned, be it through periodicity, quasi-periodicity or isostaticity. Here we show that amorphous Chern insulators can be readily constructed from arbitrary underlying structures, including hyperuniform, jammed, quasi-crystalline and uniformly random point sets. While our findings apply to mechanical and electronic systems alike, we focus on networks of interacting gyroscopes as a model system. Local decorations control the topology of the vibrational spectrum, endowing amorphous structures with protected edge modes—with a chirality of choice. Using a real-space generalization of the Chern number, we investigate the topology of our structures numerically, analytically and experimentally. The robustness of our approach enables the topological design and self-assembly of non-crystalline topological metamaterials on the micro and macro scale. Whether spatial order is required for structures that support topological modes remains unclear. Amorphous arrangements of interacting gyroscopes suggest that topology arises in materials for which the only design principle is the local connectivity.