Direct measurements of phonon–phonon scattering in liquid<sup>4</sup>He

Smith, D H S; Williams, C. D. H.; Wyatt, A. F. G.

doi:10.1088/1367-2630/9/3/052

Cited by 3 publications

(5 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…so low that the typical wave numbers are much smaller than mc/ and the bosonic branch is populated in its quasi-linear part only. In this case, the coupling amplitude A 2↔2 OnS , that would be divergent at vanishing angles for a linear dispersion relation as already pointed out in section 4.2.3, is extremely peaked around θ 2 = θ 3 = 0 with a width of order in θ 2 and θ 3 6 and a height 6 The peak width is of order because the intermediate 1/ 2 times larger than the typical amplitude at nonzero angles, as we shall see. Using conservation of energy and momentum (130), one also finds that θ 4 = O( ) over the width of the peak.…”

Section: This Leads Tosupporting

confidence: 63%

“…Contrarily to the BCS ground state (6) in which all the pairs are at rest it includes pairs of quasiparticles with nonzero centerof-mass wavevector q. This will allow us to study the gapless, phononlike, collective modes of the system and their interactions.…”

Section: Ansatz Of Moving Pairsmentioning

confidence: 99%

“…At low temperature, interactions among phonons determine their lifetime, correlation time and mean-free path. Therefore, they play a central role in transport phenomena, such as thermal conduction in dielectric solids, in hydrodynamic properties, such as temperature dependent viscosity and attenuation of sound in liquid helium, [1][2][3][4][5][6] and in macroscopic coherence properties of degenerate gases, as they determine the intrinsic DOI: 10.1002/andp.201600352 coherence time of the condensate both in bosonic and fermionic gases. [7,8] The dominant phonon decay channel differs among physical systems, and depends in particular on the curvature of the phonon excitation branch.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Three‐Phonon and Four‐Phonon Interaction Processes in a Pair‐Condensed Fermi Gas

2017

View full text Add to dashboard Cite

We study the interactions among phonons and the phonon lifetime in a pair-condensed Fermi gas in the BEC-BCS crossover in the collisionless regime. To compute the phonon-phonon coupling amplitudes we use a microscopic model based on a generalized BCS Ansatz including moving pairs, which allows for a systematic expansion around the mean field BCS approximation of the ground state. We show that the quantum hydrodynamic expression of the amplitudes obtained by Landau and Khalatnikov apply only on the energy shell, that is for resonant processes that conserve energy. The microscopic model yields the same excitation spectrum as the Random Phase Approximation, with a linear (phononic) start and a concavity at low wave number that changes from upwards to downwards in the BEC-BCS crossover. When the concavity of the dispersion relation is upwards at low wave number, the leading damping mechanism at low temperature is the Beliaev-Landau process 2 phonons ↔ 1 phonon while, when the concavity is downwards, it is the Landau-Khalatnikov process 2 phonons ↔ 2 phonons. In both cases, by rescaling the wave vectors to absorb the dependence on the interaction strength, we obtain a universal formula for the damping rate. This universal formula corrects and extends the original analytic results of Landau and Khalatnikov [ZhETF 19, 637 (1949)] for the 2 ↔ 2 processes in the downward concavity case. In the upward concavity case, for the Beliaev 1↔ 2 process for the unitary gas at zero temperature, we calculate the damping rate of an excitation with wave number q including the first correction proportional to q 7 to the q 5 hydrodynamic prediction, which was never done before in a systematic way.

show abstract

Section: This Leads Tosupporting

confidence: 63%

Section: Ansatz Of Moving Pairsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Three‐Phonon and Four‐Phonon Interaction Processes in a Pair‐Condensed Fermi Gas

2017

View full text Add to dashboard Cite

show abstract

“…However for strongly anisotropic phonon systems c << 1. Such systems can be created experimentally [14][15][16].…”

Section: Relaxation In Phonon System Caused By Four-phonon Processesmentioning

confidence: 99%

“…Here the beam of h-phonons is scattered by the isotropic distribution of thermal low-energy phonons. Recently, direct measurements of the phonon-phonon scattering rates interactions have been made by scattering two beams of phonons [14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Four- and three-phonon scattering in isotropic superfluid helium

Adamenko

Kitsenko

Nemchenko

et al. 2009

Low Temperature Physics

View full text Add to dashboard Cite

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.

show abstract