Chaotic Third Sound Resonances

Abstract

There are three independent phenomena that compete to determine the line shapes of third sound resonances in a circular cavity. First, anharmonic terms in the hydrodynamic equations of motion lead to the usual hysteresis on a mugti-valued response function. Second, wave coupling to vortices pinned in the film modify the resonant frequency as changes in the persistent current are induced. Finally, nonlinear dissipation can lead to saturation. The first two of these have been observed to resugt in continuous (not just transient) temporal behavior of the resonance amplitude with a fixed drive. Both cyclical and chaotic behaviors have been observed. The effects are dependent on the ability of the driven wave to either accelerate or decelerate the persistent current onto different amplitude branches of the mugti-valued resonance.