# Observation of topological gravity-capillary waves in a water wave crystal

## TL;DR

This paper demonstrates the first experimental observation of topological edge states in a dispersive water wave system, showing valley-locked transport in a water wave crystal supporting gravity-capillary waves.

## Contribution

It introduces a novel water wave crystal insulator that supports topological valley transport in a highly dispersive classical wave system.

## Key findings

- First experimental demonstration of topological water wave edge states
- Valley-locked water wave transport observed
- Water wave crystal supports topological domain wall transport

## Abstract

The discovery of topological phases of matter, initially driven by theoretical advances in quantum condensed matter physics, has been recently extended to classical wave systems, reaching out to a wealth of novel potential applications in signal manipulation and energy concentration. Despite the fact that many realistic wave media (metals at optical frequencies, polymers at ultrasonic frequencies) are inherently dispersive, topological wave transport in photonic and phononic crystals has so far been limited to ideal situations and proof-of-concept experiments involving dispersionless media. Here, we report the first experimental demonstration of topological edge states in a classical water wave system supporting highly dispersive wave propagation, in the intermediate regime of gravity-capillary waves. We use a stochastic method to rigorously take into account the inherent dispersion and devise a water wave crystal insulator supporting valley-selective transport at topological domain walls. Our measurements, performed with a high-speed camera under stroboscopic illumination, unambiguously demonstrate the possibility of valley-locked transport of water waves.