Roton

In theoretical physics, a roton is an elementary excitation, or quasiparticle, seen in superfluid helium-4 and Bose–Einstein condensates with long-range dipolar interactions or spin-orbit coupling.

[1][2] The observation of such a "roton-like" dispersion relation was demonstrated under ambient conditions for both acoustic pressure waves in a channel-based metamaterial at audible frequencies and transverse elastic waves in a microscale metamaterial at ultrasound frequencies.

[4] Currently there exist models which try to explain the roton spectrum with varying degrees of success and fundamentality.

[5][6] The requirement for any model of this kind is that it must explain not only the shape of the spectrum itself but also other related observables, such as the speed of sound and structure factor of superfluid helium-4.

[9] Under specific conditions the roton minimum gives rise to a crystal solid-like structure called the supersolid, as shown in experiments from 2019.