We report on experiments using energetic ultrasound pulses on superfluid 3He-B. Near the two-phonon pair breaking edge, at hf=Δ(T), an anomaly in ultrasonic attenuation has been detected. This feature grows with increasing acoustical intensity, and a new peak develops in the attenuation spectrum. The anomaly, coupling nonlinearly to ultrasound, can be observed also in the phase velocity of sound; in a magnetic field the anomaly splits to at least three features.
- nonlinear acoustics
- superfluid 3He