Observation of Momentum-Band Topology in PT-Symmetric acoustic Floquet Lattices

TL;DR

This study provides the first bulk experimental evidence of momentum-band topology in a PT-symmetric Floquet acoustic lattice, revealing topological invariants and interface states through innovative synthesis and analysis.

Contribution

It demonstrates the experimental realization and measurement of momentum-band topology in a Floquet system using acoustic structures, including the extraction of eigenstates and topological invariants.

Findings

First bulk evidence of momentum-band topology in a Floquet lattice

Observation of time-localized interface states

Quantized Berry phase characterizing the momentum gap

Abstract

Momentum-band topology, which transcends conventional topological band theory, unlocks new topological phases that host fascinating temporal interface states. However, direct bulk experimental evidence of such emerging band topology is still lacking due to the great challenges in resolving eigenstates and topological invariants of time-varying systems. Here, we present a comprehensive study on the momentum-band topology in a PT-symmetric Floquet lattice, where the drive-induced momentum gap can be characterized by a quantized Berry phase in the energy Brillouin zone. Experimentally, we synthesize the Floquet lattice model using an acoustic cavity-tube structure coupled to custom-designed external circuits. By reconstructing the effective Hamiltonian, we extract the system's eigenstates and provide the first bulk evidence of momentum-band topology from the perspectives of band inversion and topological invariants. This is accompanied by an unambiguous observation of time-localized interface states in real physical time, thereby providing the boundary signature of the bulk topology. Our work paves the way for further experimental studies on the burgeoning momentum-gap physics.