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Center for Nonlinear Studies |
Although solid 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 putative “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 toward equilibrium. These phenomena are all consistent with glass formation as proposed by the LANL group. Analysis using a generalized rotational susceptibility then 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(T) was far too large. We therefore raised the possibility that amorphous solid 4He is a "superglass" in which dynamical excitations within the solid control the superfluid phase stiffness (Science 324, 632 2009) . In that context we next considered if inertially-active excitations whose relaxation times τ(T) smoothly increase with falling temperature T can cause the observed effects when 1/τ (T) equals the torsional oscillator (TO) resonance frequency ω0. We map solid 4He rotational and relaxational dynamics throughout the velocity-temperature plane. We find them consistent with the ω0τ=1 mechanism with contributions from both thermally and mechanically stimulated excitations. Moreover τ (T) diverges smoothly with no evidence for the sudden changes signifying the critical Vc or Tc expected of a supersolid phase transition. Finally, we show that the relative influence of T and V on the rotational inertia is identical to the relative influence of T and shear strain ε on the 4He shear modulus. This implies strongly that the rotational dynamics of solid 4He are due to the generation (presumably by TO inertial shear strain for which ε ∝ V) of the same type of microscopic excitations which are generated by direct shear strain.
Host: Joe Thompson, MPA-CMMS, jdt@lanl.gov, Alexander Balatsky, T-4, avb@lanl.gov