Roton
A roton is an excitation in superfluid Helium-4.
A graph of the energy vs. the momentum of such
an excitation increases linearly from the origin,
but exhibits first a maximum and then a minimum
in energy as the momentum increases. Excitations
with momenta in the linear region are called phonons;
those with momenta close to the minimum are called
rotons. Excitations with momenta near the maximum are
sometimes called maxons.
Roton also refers to the Roton SSTO spacecraft design.
