Nonlinear ultrasonic excitations and landau damping in the Fermi liquid He-3

Pulsed sound-transmission experiments at different pressures (0-16 bars), frequencies (10-50 MHz), and sound-pulse energies (0.01-110 nJ) demonstrated that Landau damping exists in a Fermi liquid even for low-frequency phonons al temperatures as high as 1 mK due to multiple-phonon absorption. This nonlinear damping of zero sound increases with the square of the frequency. A pronounced sound power dependence of the quasiparticle collision time was found as well as an additional damping of first sound at the third harmonic frequency.