Observation of roton-like dispersion relations in acoustic metamaterials

TL;DR

This paper reports the first experimental observation of roton-like dispersion relations in acoustic metamaterials at room temperature, revealing multiple rotons and broadband backward waves, bridging quantum phenomena and classical acoustics.

Contribution

It demonstrates the realization of roton-like dispersions in acoustic metamaterials with long-range interactions, a phenomenon previously only predicted theoretically.

Findings

Observation of roton-like minima in acoustic dispersion relations

Multiple rotons appear on a single dispersion band with increased interaction range

Presence of broadband backward waves analogous to quantum rotons

Abstract

Roton dispersion relations, displaying a pronounced "roton" minimum at finite momentum, were firstly predicted by Landau and have been extensively explored in correlated quantum systems at low temperatures. Recently, the roton-like dispersion relations were theoretically extended to classical acoustics, which, however, have remained elusive in reality. Here, we report the experimental observation of roton-like dispersions in acoustic metamaterials with beyond-nearest-neighbour interactions at ambient temperatures. The resulting metamaterial supports multiple coexisting modes with different wavevectors and group velocities at the same frequency and broadband backward waves, analogous to the "return flow" termed by Feynman in the context of rotons. Moreover, by increasing the order of long-range interaction, we observe multiple rotons on a single dispersion band, which have never appeared in Landau's prediction or any other condensed matter study. The realization of roton-like dispersions in metamaterials could pave the way to explore novel physics and applications on quantum-inspired phenomena in classical systems.