Velocity dependence of supersolid He-4 in a torsion oscillator.

We have developed a free-inertial-decay mapping technique which allows us to acquire the complete velocity-temperature “phase diagram” of supersolid He-4. A striking new feature of the resulting supersolid response map is the appearance of an enhanced dissipation superpeak. We discuss these results in context of various microscopic mechanisms for the velocity-induced suppression of the supersolid response, including a superfluid critical velocity, defect network critical shear, and a glassy dynamical susceptibility.