Anomalous sound absorption of finite amplitude sound in liquid ⁴He

We report the nonlinear and unsteady response of the finite amplitude pressure wave in superfluid ⁴He, using a classical vibrating liquid column standing wave resonator. The frequency was kept at the resonance frequency of the liquid column, so that the maximum of the pressure field always came to the surface of the driver. As a result, in the low driving-amplitude regime, I/O relations were linear. However, in the high driving-amplitude regime, anomalous responses were found; The amplitude of the signals suddenly reduced and gradually recovered; they were repeated with random intervals. Moreover, in the highly suppressed region in the waveform, we found a generation of new type of turbulence. These absorptions are expected to be the result of the vapor bubble ejection from the surface of the driver transducer.