  Supersolid helium has a rather low transition temperature and a small
critical velocity, compared with liquid helium. These properties could be
explained in terms of helium's spectrum structure and quantum jumps involving
large momentum transfer. A grain in the solid helium possess valleys (local
minima) in its many-body dispersion curve, and an exchange of large momenta
with the grain's surroundings occurs in a jump between a level in one valley
and another level in the neighboring valley. Such jump process also naturally
causes dissipation accompanying the onset of supersolidity.
