[en] This is a brief survey of the role of physical acoustics in exploring the superconducting and more particularly the superfluid state. The nature of 1st, 2nd, 3rd, 4th, and 5th sound, and ways in which they are used to measure superfluid properties are described

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[en] The cited reports discuss superfluidity in liquid helium, with both helium 3 and helium 4 considered. Topics discussed include phase studies, heat transfer, hydrodynamics, rotons, zero sound, first sound, second sound, third sound, and fourth sound

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[en] On the basis of a set of kinetic equations for the matrix distribution function of a pair-correlated Fermi liquid derived previously, the dispersion law of sound is calculated for arbitrary values of ωtau (tau is a collision time) and for all temperatures. The collision operator is approximated by a sum of energy-dependent relaxation-time expressions, such that the conservation laws are guaranteed and the important 1=2 component is preserved. The result agrees with exact solutions of the Boltzmann equation, wherever those are available, apart from irrelevant higher-order terms in the eigenvalue expansion. The principal results are (I) a simple relaxation-time expression is found to describe the attenuation and velocity of sound in the normal state at arbitrary ωtau; (II) the relevant relaxation times in the superfluid are computed from the microscopic theory in the vicinity of the transition and for tempertures tending to zero; (III) the calculated attenuation and velocity of zero sound in the pseudoisotropic state are in good agreement with available data in the B phase of ³He. A value for the quasiparticle lifetime at the Fermi surface is obtained from the broadening of the collective-mode peak in the attenuation. It is found that the value of the 1 = 2 component of the collision integral near the polycritical point of ³He required to fit the data is smaller than theoretical predictions by a factor of 1.7, pointing to a possible source of the existing discrepancy between viscosity data theory (iv) The viscosity coefficient in the pseudoisotropic state is derived from the hydrodynamic sound attenuation for all temperatures. The change of the viscosity in the superfluid is found to be proportional to 1 - T/T/sub c/ near the transition due to a pair-breaking effect not included in previous theories

[en] The equations describing the propagation of the first, second and fourth sound in the relativistic theory of superfluidity are derived with account for dissipation. The expressions for the velocity of the first, second and fourth sound are obtained. (author). 4 refs

[en] The microscopic theory of liquid helium II due to Fliessbach [T. Fliessbach, Nuovo Cimento D 13, 211 (1991)] allows a certain amount of entropy to be carried by the superfluid component. The experimental results tell us that the entropy carried by the superfluid component is smaller than 2% with respect to the total entropy. The nonstandard model of liquid helium II deduced from extended thermodynamics is not in contrast with the theory by Fliessbach. In this work, using this model, we show that accurate measurements of the speeds and the attenuations of the first, second, and fourth sounds in liquid helium II allow the determination of this small superfluid entropy, or, at least, they will establish an upper bound for this quantity

[en] In Part I of this series, a theory of helium II incorporating the effects of quantum healing and relaxation was developed. In this paper, the propagation of first, second, and fourth sound is discussed. Particular attention is paid to sound propagation in the vicinity of the lambda point where the effects of relaxation and quantum healing become important

[en] In the spirit of the Landau theory of Fermi liquid, the paper considers the solution of an isotropic superfluid Fermi liquid in a superfluid Bose liquid. On the basis of the kinetic equation for the Fermi particle distribution function, a three-velocity hydrodynamics for such a solution has been derived in the limit of ωtau < < 1. There have been obtained sonic solutions of hydrodynamics equations; temperature dependences have been investigated of velocities of the first, second, third and two fourth sounds under all temperatures. In the high frequency limit ωtau > > 1 there have been obtained two sonic solutions of the kinetic equation, one of which with T > Tsub(c) turns into a zero sound in a solution of a normal Fermi liquid in a Bose liquid. All physical values have been expressed through Fermi liquid constants. There has been considered the problem of critical rates of a solution of a superfluid Fermi liquid in a superfluid Bose liquid