Insensitive nonreciprocal edge breathers

TL;DR

This paper explores how nonlinearity and nonreciprocity interact in topological mechanical metamaterials, revealing robust edge-localized waves called NEBs that maintain their frequency despite increasing nonlinearity, without needing symmetry protections.

Contribution

It introduces the concept of insensitive nonreciprocal edge breathers in a topological Klein-Gordon chain, demonstrating their persistence and frequency stability in nonlinear regimes.

Findings

Discovery of continuous families of nonreciprocal edge breathers.

Identification of insensitive NEBs with fixed nonlinear frequency.

Exponential decay of frequency shift with system size.

Abstract

We uncover subtle and previously unexplored phenomena arising from the interplay of nonlinearity and nonreciprocity in topological mechanical metamaterials. We study a nonreciprocal topological Klein-Gordon chain of asymmetrically coupled nonlinear oscillators, which serves as a minimal mass-spring model capturing the features of several active nonreciprocal metamaterials across mechanical, electronic, and acoustic platforms. We demonstrate that continuous families of nonreciprocal edge breathers (NEBs), namely boundary-localized, time-periodic waves, emerge from the linear edge mode as its amplitude increases. Remarkably, despite the absence of chiral or sublattice symmetries, we identify insensitive NEBs whose nonlinear frequency remains fixed to that of the linear edge mode with increasing nonlinearity. Our analysis reveals that the mechanism underlying this insensitivity stems from a competition between mode nonorthogonality and nonlinear interactions, yielding an exponential decay of the NEB nonlinear frequency shift with system size. Crucially, these insensitive NEBs also persist in the strongly nonlinear regime. Our work establishes a novel pathway toward realizing robust nonlinear topological waves in mechanical metamaterials without relying on symmetry-protected nonlinearities.