Viscosity and relaxation processes in the phonon-roton system of He II

Zadorozhko, A. A.; Rudavskiı̆, É. Ya.; Chagovets, V. K.; Sheshin, G. A.; Kitsenko, Yu. A.

doi:10.1063/1.3075937

Cited by 20 publications

(35 citation statements)

References 15 publications

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“…However, it has been observed experimentally that for 4 He at very low temperature ballistic phonons can still efficiently damp the movement of immersed objects, see Refs. [47][48][49]. This damping can still be described by an effective or ballistic shear viscosity coefficient defined by ball 1 5 ph c s d; (2.18) where d is the typical size of the oscillating object, and is a coefficient that measures the probability that the phonons are diffused at the boundary with the object.…”

Section: B Shear Viscosity Due To Phonons In Superfluid Neutrons Stamentioning

confidence: 99%

Shear viscosity and ther-mode instability window in superfluid neutron stars

Manuel

Tolós²

2013

Phys. Rev. D

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We analyze how recent computations of the shear viscosity in the core of superfluid neutron stars affect the r-mode instability window. We first analyze the contribution of superfluid phonons to the viscosity, both in their hydrodynamical and ballistic regime. We also consider the recent computation of arising from the collisions of electrons with electrons and protons by Shternin and Yakovlev, and discuss how the interactions among superfluid phonons and electrons might contribute to the shear viscosity. For assessing the r-mode instability window we compare the shear viscosity due to phonons in the hydrodynamical regime with respect to the shear viscosity due to electron collisions. Only at high temperatures the superfluid phonon contribution to starts to dominate the process of r-mode damping. While our results for the instability window are preliminary, as other dissipative processes should be taken into account as well, they differ from previous evaluations of the r-mode damping due to the shear viscosity in superfluid neutron stars.

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Section: B Shear Viscosity Due To Phonons In Superfluid Neutrons Stamentioning

confidence: 99%

Shear viscosity and ther-mode instability window in superfluid neutron stars

Manuel

Tolós²

2013

Phys. Rev. D

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“…However in this temperature region, there is a considerable contribution to the viscosity coefficient from phonon-roton interactions and it is necessary to take these processes into account. The deviation of the experimental points [24,25] from the theoretical curve at temperatures higher 0.7 K is due exactly to ignoring these phonon-roton interactions. In the intermediate temperature range (from 0.5 to 0.9 K) the contributions of three-phonon and four-phonon relaxation have the same order of magnitude and both processes should be taken into account for calculating the first viscosity coefficient.…”

Section: Calculation Of the Contribution Of Small And Large Angle Scamentioning

confidence: 88%

“…We note, that for the A quantities the following relations are valid ; curve 3 is a numerical calculation of the relaxation time from Eq. (59) without the contribution of small angles between p 1 and p 2 (i.e., the lower limit of integration over angles is equal to 30°); experimental points from Greywall [24] are marked by triangles, the squares show the experimental data from Zadorozhko et al [25].…”

Section: Calculation Of the Contribution Of Small And Large Angle Scamentioning

confidence: 99%

Four- and three-phonon scattering in isotropic superfluid helium

Adamenko

Kitsenko

Nemchenko

et al. 2009

Low Temperature Physics

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We analyse the important role of four-phonon processes (4pp) in isotropic phonon systems of superfluid helium. The matrix elements and the rate of four-phonon processes are calculated. Special consideration is given to the 4pp in the momentum range where three-phonon processes are allowed. In this momentum range, we show that the 4pp scattering rate, at small angles, is equal to the scattering rate due to three-phonon processes. Then we show that the coefficient of first viscosity of superfluid helium is caused by two processes, the first is due to the transverse relaxation caused by many three-phonon processes and the second is due to four-phonon processes. The relaxation time that governs the viscosity is obtained from the sum of the rates from these two processes. The temperature dependence of the attenuation coefficient of a pulse of high-energy phonons in He II, due to scattering with thermal phonons, is also calculated. The theoretical results are compared with experimental data and found to be in good agreement. PACS: 47.37.+q Hydrodynamic aspects of superfluidity; quantum fluids.

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“…There are cases, however, when small-angle collisions may dominate, as it may turn out to be more efficient to achieve a large-angle collision by the addition of many small-angle scatterings. In the low T regime of superfluid 4 He where the viscosity is dominated by phonons, the 4-ph large-angle collisions give the leading contribution to the shear viscosity only in a restricted range of temperature [42], while 3-ph small-angle processes dominate for any temperature below 0.7 K [16].…”

Section: Shear Viscosity Due To Small-angle Collisionsmentioning

confidence: 99%

Phonon contribution to the shear viscosity of a superfluid Fermi gas in the unitarity limit

2013

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We present a detailed analysis of the contribution of small-angle Nambu-Goldstone boson (phonon) collisions to the shear viscosity, η, in a superfluid atomic Fermi gas close to the unitarity limit. We show that the experimental values of the shear viscosity coefficient to entropy ratio, η/s, obtained at the lowest reached temperature can be reproduced assuming that phonons give the leading contribution to η. The phonon contribution is evaluated considering 1 ↔ 2 processes and taking into account the finite size of the experimental system. In particular, for very low temperatures, T < ∼ 0.1TF , we find that phonons are ballistic and the contribution of phonons to the shear viscosity is determined by the processes that take place at the interface between the superfluid and the normal phase. This result is independent of the detailed form of the phonon dispersion law and leads to two testable predictions: the shear viscosity should correlate with the size of the optical trap and it should decrease with decreasing temperature. For higher temperatures the detailed form of the phonon dispersion law becomes relevant and, within our model, we find that the experimental data for η/s can be reproduced assuming that phonons have an anomalous dispersion law.

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Viscosity and relaxation processes in the phonon-roton system of He II

Cited by 20 publications

References 15 publications

Shear viscosity and ther-mode instability window in superfluid neutron stars

Shear viscosity and ther-mode instability window in superfluid neutron stars

Four- and three-phonon scattering in isotropic superfluid helium

Phonon contribution to the shear viscosity of a superfluid Fermi gas in the unitarity limit

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