Thermal conductivity and viscosity via phonon-phonon, phonon-roton, and roton-roton scattering in thin<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>films

Um, Chung-In; Jun, Chul-Won; Kahng, W. H.; George, Thomas F.

doi:10.1103/physrevb.38.8838

Cited by 8 publications

(5 citation statements)

References 20 publications

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“…There were consistent with the existing observations of the "effective" viscosity associated with the drag force [27]. An estimation of η n was adopted from the preceding studies [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], which is divided into the contributions from phonons and rotons, η n = η ph + η ro [31]. While the roton part η ro is dominant and independent on T for 1 < T 1.5 K, the phonon part η ph is important below 0.7 K and increases with decreasing temperature; η ph = 1 5 ρ n u 2 ph τ ph with ρ n ∝ T 4 and τ ph ∝ T −5 for T → 0.…”

Section: Fnsupporting

confidence: 57%

“…Accordingly, F D is divided into two contributions, F n and F s , from the normal fluid and superfluid components, respectively; F D = F n + F s . The kinematic viscosity ν n of the normal fluid component has been well studied [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and the normal Reynolds number is R n = ud νn . At zero temperature (T = 0), only superfluid component exists with the body never experiencing the drag force F D = 0 as known as the D'Alembert's paradox [2] [Fig.…”

Section: Drag Coefficientsmentioning

confidence: 99%

“…The form of the dynamic viscosity below 1.5 K is determined according to the preceding works [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. The normal viscosity η n is divided into two parts as η n = η ph +η ro with the phonon viscosity η ph and the roton viscosity η ro .…”

Section: Normal Viscosity In the Hydrodynamic Regimesmentioning

confidence: 99%

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Quantum viscosity and the Reynolds similitude in quantum liquid He-II

Takeuchi¹

2023

Preprint

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Reynolds similitude, a key concept in hydrodynamics, states that two phenomena of different length scales with a similar geometry are physically identical. Flow properties are universally determined in a unified way in terms of the Reynolds number R (dimensionless, ratio of inertial to viscous forces in incompressible fluids). For example, the drag coefficient cD of objects with similar shapes moving in fluids is expressed by a universal function of R. Certain studies introduced similar dimensionless numbers, that is, the superfluid Reynolds number Rs, to characterize turbulent flows in superfluids. However, the applicablity of the similitude to inviscid quantum fluids is nontrivial as the original theory is applicable to viscous fluids. This study proposed a method to verify the similitude using current experimental techniques in quantum liquid He-II. A highly precise relation between cD and Rs was obtained in terms of the terminal speed of a macroscopic body falling in He-II at finite temperatures across the Knudsen (ballistic) and hydrodynamic regimes of thermal excitations. Reynolds similitude in superfluids can facilitate unified mutual development of classical and quantum hydrodynamics.

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Section: Fnsupporting

confidence: 57%

Section: Drag Coefficientsmentioning

confidence: 99%

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Quantum viscosity and the Reynolds similitude in quantum liquid He-II

Takeuchi¹

2023

Preprint

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“…We have explicitly checked that when this formalism is applied to phonons it is equivalent to the usual approach based on a P (X) effective field theory. We also considered phonon-roton scattering, and corrected earlier result by Landau and Khalatnikov as well as subsequent calculations based on similar techniques [25,26]. Since an alternative EFT approach to rotons is presently not available, it is our hope that experiments will soon be able to weigh in on this discrepancy, given that interactions between phonons and rotons have already been the subject of very interesting experimental work [27,28,29].…”

Section: Discussion and Outlookmentioning

confidence: 99%

Mutual interactions of phonons, rotons, and gravity

Nicolis

Penco

2018

Phys. Rev. B

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We introduce an effective point-particle action for generic particles living in a zerotemperature superfluid. This action describes the motion of the particles in the medium at equilibrium as well as their couplings to sound waves and generic fluid flows. While we place the emphasis on elementary excitations such as phonons and rotons, our formalism applies also to macroscopic objects such as vortex rings and rigid bodies interacting with long-wavelength fluid modes. Within our approach, we reproduce phonon decay and phonon-phonon scattering as predicted using a purely field-theoretic description of phonons. We also correct classic results by Landau and Khalatnikov on roton-phonon scattering. Finally, we discuss how phonons and rotons couple to gravity, and show that the former tend to float while the latter tend to sink but with rather peculiar trajectories. Our formalism can be easily extended to include (general) relativistic effects and couplings to additional matter fields. As such, it can be relevant in contexts as diverse as neutron star physics and light dark matter detection. arXiv:1705.08914v1 [hep-th]

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“…9 The transition amplitude between the temperature-dependent initial state II> and final state IF> for the direct process is given by…”

Section: -mentioning

confidence: 99%