Complete absorption of topologically protected waves

TL;DR

This paper demonstrates how topological interface design can trap and dissipate energy in fluid systems, offering new approaches for acoustic absorption and soundproofing by exploiting mode disappearance and non-Hermiticity.

Contribution

It introduces a novel interface design in topological fluids that traps modes and enhances energy dissipation, linking topology with non-Hermitian effects.

Findings

Explicit expressions for disappearing modes in fluid systems.

Energy dissipation is increased by mode trapping.

Topology can be used for acoustic shielding applications.

Abstract

Chiral edge states can transmit energy along imperfect interfaces in a topologically robust and unidirectional manner when protected by bulk-boundary correspondence. However, in continuum systems, the number of states at an interface can depend on boundary conditions. Here we design interfaces that host a net flux of the number of modes into a region, trapping incoming energy. As a realization, we present a model system of two topological fluids composed of counter-spinning particles, which are separated by a boundary that transitions from a fluid-fluid interface into a no-slip wall. In these fluids, chiral edge states disappear, which implies non-Hermiticity and leads to a novel interplay between topology and energy dissipation. Solving the fluid equations of motion, we find explicit expressions for the disappearing modes. We then conclude that energy dissipation is sped up by mode trapping. Instead of making efficient waveguides, our work shows how topology can be exploited for applications towards acoustic absorption, shielding, and soundproofing.