Isospectral reduction of the SSH3 lattice and its bulk-edge correspondence

TL;DR

This paper introduces an isospectral reduction method for the SSH3 lattice that simplifies the model while preserving its topological properties, enabling control over topological phase transitions and experimental verification.

Contribution

The study develops a novel isospectral reduction approach for SSH3 lattices, linking bulk properties to band topology and demonstrating topological phase control through energy-dependent couplings.

Findings

Successful reduction of SSH3 lattice to a two-site model

Experimental observation of topological edge states in an acoustic chain

Control of topological phase transition via energy-dependent couplings

Abstract

Here, we propose an isospectral reduction (IR) approach for the mapping of a trimer Su-Schrieffer-Heeger (SSH3) lattice into a simplified two-site model, whose coupling dynamics ingeniously results in a precise bulk-edge correspondence of the original lattice. The isospectrally-reduced model has inter-cell couplings with dynamic response to the eigenstate energy, allowing for the control of topological phase transition by energy. We relate the bulk property of the reduced model to the band topology of the SSH3 lattice, allowing for there distinct topological phases with different number of topological edge state pair. An acoustic SSH3 chain is fabricated for experimental demonstration. The said topological edge state pairs are measured. Our study takes a pivotal step toward the exploration of topology in multiple wave systems, opening up possibilities for advanced control of topological waves.