  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.
