Experimental realization of on-chip topological nanoelectromechanical metamaterials.

Abstract

Guiding waves through a stable physical channel is essential for reliable information transport. However, energy transport in high-frequency mechanical systems, such as in signal-processing applications¹, is particularly sensitive to defects and sharp turns because of back-scattering and losses². Topological phenomena in condensed matter systems have shown immunity to defects and unidirectional energy propagation³. Topological mechanical metamaterials translate these properties into classical systems for efficient phononic energy transport. Acoustic and mechanical topological metamaterials have so far been realized only in large-scale systems, such as arrays of pendulums⁴, gyroscopic lattices^5,6, structured plates^7,8 and arrays of rods, cans and other structures acting as acoustic scatterers^9-12. To fulfil their potential in device applications, mechanical topological systems need to be scaled to the on-chip level for high-frequency transport^13-15. Here we report the experimental realization of topological nanoelectromechanical metamaterials, consisting of two-dimensional arrays of free-standing silicon nitride nanomembranes that operate at high frequencies (10-20 megahertz). We experimentally demonstrate the presence of edge states, and characterize their localization and Dirac-cone-like frequency dispersion. Our topological waveguides are also robust to waveguide distortions and pseudospin-dependent transport. The on-chip integrated acoustic components realized here could be used in unidirectional waveguides and compact delay lines for high-frequency signal-processing applications.