Self-ordering induces multiple topological transitions for elastic waves in phononic crystals

TL;DR

This paper introduces an elastic topological insulator that exhibits multiple topological transitions, enabling robust elastic wave transport through symmetry-breaking and topological defect manipulation in a phononic crystal.

Contribution

It presents a novel elastic topological insulator with spontaneously broken symmetry, demonstrating multiple topological transitions and robust edge states in a phononic crystal.

Findings

Multiple topological transitions achieved by modifying ellipse orientation.

Experimental demonstration of robust edge state transport.

Breakthrough in elastic wave control via topological defect theory.

Abstract

Topological defects with symmetry-breaking phase transitions have captured much attention. Vortex generated by topological defects exhibits exotic properties and its flow direction can be switched by altering the spin configurations. Contrary to electromagnetic and acoustic domains, the topological transport of elastic waves in periodic structures with topological defects is not well explored due to the mode conversion between the longitudinal and transverse modes. Here, we propose an elastic topological insulator with spontaneously broken symmetry based on the topological theory of defects and homotopy theory. Multiple topological transitions for elastic waves are achieved by topologically modifying the ellipse orientation in a triangular lattice of elliptical cylinders. The solid system, independent of the number of molecules in order parameter space, breaks through the limit of the point-group symmetry to emulate elastic pseudospin-orbit coupling. The transport robustness of the edge states is experimentally demonstrated. Our approach provides new possibilities for controlling and transporting elastic waves.