Experimental study of the nonlinear second sound wave interaction in superfluid 4He.

We report preliminary results of investigations of the nonlinear second sound wave interaction in a high-quality resonator filled with superfluid 4He. The anomalously large nonlinear coefficient of second sound allows us to observe the formation of higher harmonics while pumping the resonator at a resonant frequency and, in this manner, to study wave energy transfer from the low-frequency domain to the high-frequency domain over a wide frequency range. The observed nonequilibrium stationary wave distribution of amplitudes A f for multiple harmonics over wave frequency f may be described as , where s ≥ 1.5.