Experimental observation of roton-like dispersion relations in metamaterials

Previously, rotons were observed in correlated quantum systems at low temperatures, including superfluid helium and Bose-Einstein condensates. Here, following a recent theoretical proposal, we report the direct experimental observation of roton-like dispersion relations in two different three-dimensional metamaterials under ambient conditions. One experiment uses transverse elastic waves in microscale metamaterials at ultrasound frequencies. The other experiment uses longitudinal air-pressure waves in macroscopic channel-based metamaterials at audible frequencies. In both experiments, we identify the roton-like minimum in the dispersion relation that is associated to a triplet of waves at a given frequency. Our work shows that designed interactions in metamaterials beyond the nearest neighbors open unprecedented experimental opportunities to tailor the lowest dispersion branch-while most previous metamaterial studies have concentrated on shaping higher dispersion branches.

Automated summary

The research reports the direct experimental observation of roton-like dispersion relations in two different three-dimensional metamaterials under ambient conditions. Two different experiments using ultrasound and audible frequencies respectively were conducted to identify the roton-like minimum in the dispersion relation associated to a triplet of waves at a given frequency. The work demonstrates that designing interactions in metamaterials beyond the nearest neighbors can open unprecedented experimental opportunities to tailor the lowest dispersion branch.