title: Frequency dependence and dissipation in the dynamics of solid helium.
abstract: Torsional oscillator experiments on solid 4He show frequency changes which suggest mass decoupling, but the onset is broad and is accompanied by a dissipation peak. We have measured the elastic shear modulus over a broad frequency range, from 0.5 Hz to 8 kHz, and observe similar behavior-stiffening and a dissipation peak. These features are associated with a dynamical crossover in a thermally activated relaxation process in a disordered system rather than a true phase transition. If there is a transition to a dc response, e.g., to a supersolid state, it must occur below 55 mK.
authors.affiliation: Department of Physics, University of Alberta, Edmonton, Alberta T6G 2G7, Canada.
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Syshchenko
authors.forename: James
authors.initials: J
authors.lastname: Day
authors.forename: John
authors.initials: J
authors.lastname: Beamish