Creation of High-Energy Phonons from Low-Energy Phonons in Liquid Helium

Adamenko, I. N.; Nemchenko, K. E.; Жуков, А. В.; Tucker, M. A. H.; Wyatt, A. F. G.

doi:10.1103/physrevlett.82.1482

Cited by 48 publications

(48 citation statements)

References 10 publications

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“…There is already some indirect evidence for this picture: the creation of high energy phonons, (h-phonons) with energy >10K can be explained by four phonon interactions between the low energy phonons (l-phonons) within the pulse. Several properties of these h-phonons have been measured [10, 11,12] and modelled theoretically [6,7,13]. Recently, it has been found experimentally that the temperature of the phonon distribution is uniform in the centre and decreases towards the edges of the pulse [14] and this behaviour can also be explained within this picture [15].…”

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confidence: 56%

“…However it was recognised that phonons could spontaneously decay by the three phonon process (3pp) [2,3], which is allowed by the upward curvature of the dispersion curve [4,5]. This picture was challenged recently by Adamenko et al [6,7] who argued that a number of observations, such as the creation of high energy phonons in the liquid, could be explained if the phonons in the pulse were treated as strongly interacting and were confined to a narrow cone in momentum space. This has prompted us to look for evidence of the proposed phonon momentum distribution.…”

mentioning

confidence: 90%

“…It was proposed [6,7], that the phonons in the This shows the bolometer signals for the two separate pulses, dashed-dot lines, and for the double pulse, solid line. the sharp peak at 40 µs is due to the l-phonons and the signal after ≈ 43µs is due to h-phonons.…”

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confidence: 99%

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Interactions between Sheets of Phonons in LiquidHe4

2003

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We have created two sheets of ∼1 K phonons in liquid 4 He at ∼55 mK such that they intersect each other as they move towards a common point. If the two sheets have a small angle between them, they interact strongly and create a hot line in the liquid helium. This line is continuously fed with energy from the two sheets and loses energy by creating high energy phonons. If the angle between the sheets is larger than ∼ 30 • they do not interact but pass through each other. These results give direct evidence for the composition of the sheets: they comprise strongly interacting low-energy phonons which occupy a narrow cone in momentum space.Phonon pulses have been created in cold liquid 4 He over many years since the initial work of Gernsey and Luszczynski in 1971 [1]. The pulses were found to travel at the velocity of sound and so it was believed, that to first order, the phonons were independent, non-interacting ballistic wave packets. The liquid 4 He was sufficiently cold that the ambient thermal phonons could be ignored. However it was recognised that phonons could spontaneously decay by the three phonon process (3pp) [2, 3], which is allowed by the upward curvature of the dispersion curve [4,5]. This picture was challenged recently by Adamenko et al. [6,7] who argued that a number of observations, such as the creation of high energy phonons in the liquid, could be explained if the phonons in the pulse were treated as strongly interacting and were confined to a narrow cone in momentum space. This has prompted us to look for evidence of the proposed phonon momentum distribution.A short electrical pulse in a planar thin-film heater is usually used to create a pulse of phonons. It was proposed [6,7], that the phonons in the 1

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Interactions between Sheets of Phonons in LiquidHe4

2003

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“…These h phonons are created by a pulse of l phonons, which has a temperature an order of magnitude less than the energy of the high-energy phonons that it creates. The theory of this unique phenomenon was proposed in [21,22]. A further development of the theory [23][24][25][26][27][28], shows that in strongly anisotropic phonon systems there exists an asymmetry between processes of creation and decay for the h phonons.…”

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On the suprathermal distribution in an anisotropic phonon system in He II

Adamenko

Nemchenko

Wyatt

2003

Low Temperature Physics

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The equation that describes the suprathermal distribution of high-energy phonons (h phonons) created in anisotropic phonon systems in superfluid helium is obtained. The solution of this equation enables the derivation of the value of suprathermal ratio S as the ratio of the actual distribution to the Bose-Einstein one, its dependences on the momentum of the h phonons, the anisotropy parameters, and the temperature of the low-energy phonons from which the h phonons are created. We analyze this equation to obtain an estimate of the value of the ratio between the h-phonon number density in anisotropic and isotropic phonon systems and draw conclusions about the dependence of S on the relevant parameters.

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“…The dependence D ) ( t shown in Fig. 9 is close to that obtained in [7,8], which was derived with the approximate cone distribution function (10), and with corresponding values of T p and z p .…”

Section: Evolution Of a Short L-phonon Pulse Caused By H-phonon Creationmentioning

confidence: 50%

Creation of high-energy phonons by four-phonon processes in anisotropic phonon systems of HeII

Adamenko

Nemchenko

Slipko

et al. 2007

Low Temperature Physics

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The problem of the creation of high-energy phonons (h-phonons) by a pulse of low-energy phonons (l-phonons) moving from a heater to a detector in superfluid helium, is solved. The rate of h-phonon creation is obtained and it is shown that created h-phonons occupy a much smaller solid angle in momentum space, than the l-phonons. An analytical expression for the creation rate of h-phonon, along the symmetry axis of a pulse, are derived. It allows us to get useful approximate analytical expressions for the creation rate of h-phonons. The time dependences of the parameters which describe the l-phonon pulse are obtained. This shows that half of the initial energy of l-phonon pulse can be transferred into h-phonons. The results of the calculations are compared with experimental data and we show that this theory explains a number of experimental results. The value of the momentum, which separates the l-and h-phonon subsystems, is found.

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Creation of High-Energy Phonons from Low-Energy Phonons in Liquid Helium

Cited by 48 publications

References 10 publications

Interactions between Sheets of Phonons in LiquidHe4

Interactions between Sheets of Phonons in LiquidHe4

On the suprathermal distribution in an anisotropic phonon system in He II

Creation of high-energy phonons by four-phonon processes in anisotropic phonon systems of HeII

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