Shear viscosity and parameters of kinetic processes in superfluid helium

Esel'son, B.N.; Nosovitskaya, O.S.; Pogorelov, L.A.; Соболев, В. И.

doi:10.1016/0378-4363(81)90327-2

Cited by 6 publications

(4 citation statements)

References 4 publications

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“…The temperature of the cell was measured by the calibrated resistive thermometer (carbon composition resistor, Allen-Bradley) placed near the cell. The measured temperature was in a good agreement (within 0.03 K) with the mixture saturated vapor pressure data [28].…”

Section: Aerogel Samplessupporting

confidence: 77%

Anisotropic reduced diffusion in dilute liquid ³He–⁴He mixture in ordered aerogel

Safiullin¹,

Kuzmin²,

Stanislavovas³

et al. 2020

J. Phys.: Condens. Matter

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We report on the first observation of 3He diffusion anisotropy in 3He–4He liquid mixture confined in ordered aerogels at 1.5–4.2 K temperatures. The used aerogels are arrays of long Al2O3 parallel 8 nm strands. The possible origins of diffusion anisotropy are considered and the changes of roton properties introduced by parallel aerogel strands are discussed. Among the responsible mechanisms we account for Knudsen diffusion, potential anisotropy of layer mode excitations or of bulklike excitations, and helium vortices. The observed reduced 3He diffusion in aerogels is discussed and suggested to appear due to helium excitations at strong confinement conditions. These observations pave the way for future experiments to gain insight into the crossover regime expected at lower temperatures (below 1 K) for which roton density is lower and 3He collisions with strands play significant role.

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Section: Aerogel Samplessupporting

confidence: 77%

Anisotropic reduced diffusion in dilute liquid ³He–⁴He mixture in ordered aerogel

Safiullin¹,

Kuzmin²,

Stanislavovas³

et al. 2020

J. Phys.: Condens. Matter

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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…”

Section: B Shear Viscosity Due To Phonons In Superfluid Neutrons Star...mentioning

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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“…The same phenomenon takes place in 4 He at extremely low temperature, T < ∼ 0.5 K, where it has been observed that ballistic phonons can efficiently damp the movement of immersed objects. Experiments done with an oscillating sphere [53], a vibrating microsphere [54], or a vibrating quartz tuning fork [42] immersed in superfluid 4 He (see [42] also for a comparison of the results obtained with various experimental apparatuses) show that the damping of the oscillations can be described, in perfect accommodation (χ = 1), by the introduction of a ballistic (effective) shear viscosity coefficient defined by…”

Section: A Finite Size Effectsmentioning

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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Shear viscosity and parameters of kinetic processes in superfluid helium

Cited by 6 publications

References 4 publications

Anisotropic reduced diffusion in dilute liquid ³He–⁴He mixture in ordered aerogel

Anisotropic reduced diffusion in dilute liquid ³He–⁴He mixture in ordered aerogel

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

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

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Shear viscosity and parameters of kinetic processes in superfluid helium

Cited by 6 publications

References 4 publications

Anisotropic reduced diffusion in dilute liquid 3He–4He mixture in ordered aerogel

Anisotropic reduced diffusion in dilute liquid 3He–4He mixture in ordered aerogel

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

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

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Anisotropic reduced diffusion in dilute liquid ³He–⁴He mixture in ordered aerogel

Anisotropic reduced diffusion in dilute liquid ³He–⁴He mixture in ordered aerogel