  Although solid helium-4 (4He) may be a supersolid it also exhibits many
phenomena unexpected in that context. We studied relaxation dynamics in the
resonance frequency f(T) and dissipation D(T) of a torsional oscillator
containing solid 4He. With the appearance of the "supersolid" state, the
relaxation times within f(T) and D(T) began to increase rapidly together. More
importantly, the relaxation processes in both D(T) and a component of f(T)
exhibited a complex synchronized ultraslow evolution towards equilibrium.
Analysis using a generalized rotational susceptibility revealed that, while
exhibiting these apparently glassy dynamics, the phenomena were quantitatively
inconsistent with a simple excitation freeze-out transition because the
variation in f was far too large. One possibility is that amorphous solid 4He
represents a new form of supersolid in which dynamical excitations within the
solid control the superfluid phase stiffness.
