Hysteretic Response of Torsionally Oscillated Solid 4He and Its Dependence on 3He Impurity Concentration

Measurements on hysteretic response of compound torsional oscillator containing annular-shaped solid ⁴He samples were carried out by varying the oscillator drive amplitude starting from high to low and then back up to the initial high value. Hysteresis in the oscillator frequency and amplitudes were observed only below an onset temperature. The hysteresis onset temperature (T _H ) did not depend on the oscillator frequency, width of the sample annulus, annealing and refreezing after melting. A systematic increase in T _H was observed as the ³He impurity concentration in solid ⁴He samples was increased. The dependence of T _H on ³He impurity concentration followed approximately that of the dissipation peak temperatures. Possible relationships of the observed hysteresis phenomena with models of solid ⁴He dynamics based on freezing of a vortex liquid and dislocation motion are discussed.