Zero sound

Zero sound is the name given by Lev Landau in 1957 to the unique quantum vibrations in quantum Fermi liquids.^[1] The zero sound can no longer be thought of as a simple wave of compression and rarefaction, but rather a fluctuation in space and time of the quasiparticles' momentum distribution function. As the shape of Fermi distribution function changes slightly (or largely), zero sound propagates in the direction for the head of Fermi surface with no change of the density of the liquid. Predictions and subsequent experimental observations of zero sound^[2]^[3]^[4] was one of the key confirmation on the correctness of Landau's Fermi liquid theory.

^ Landau, L. D. (1957). Oscillations in a Fermi liquid. Soviet Physics Jetp-Ussr, 5(1), 101-108.
^ Keen, B. E., Matthews, P. W., & Wilks, J. (1965). The acoustic impedance of liquid helium-3. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 284(1396), 125-136.
^ Abel, W. R., Anderson, A. C., & Wheatley, J. C. (1966). Propagation of zero sound in liquid He 3 at low temperatures. Physical Review Letters, 17(2), 74.
^ Roach, P. R., & Ketterson, J. B. (1976). Observation of Transverse Zero Sound in Normal He 3. Physical Review Letters, 36(13), 736.

[1] Landau, L. D. (1957). Oscillations in a Fermi liquid. Soviet Physics Jetp-Ussr, 5(1), 101-108.

[2] Keen, B. E., Matthews, P. W., & Wilks, J. (1965). The acoustic impedance of liquid helium-3. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 284(1396), 125-136.

[3] Abel, W. R., Anderson, A. C., & Wheatley, J. C. (1966). Propagation of zero sound in liquid He 3 at low temperatures. Physical Review Letters, 17(2), 74.

[4] Roach, P. R., & Ketterson, J. B. (1976). Observation of Transverse Zero Sound in Normal He 3. Physical Review Letters, 36(13), 736.

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