Thermodynamics of anisotropic phonon systems in superfluid helium

Adamenko, I. N.; Nemchenko, K. E.; Slipko, V. A.; Wyatt, A. F. G.

doi:10.1088/0953-8984/18/10/006

Cited by 9 publications

(15 citation statements)

References 17 publications

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“…Figure 3 shows the angular dependences of the amplitudes T c / ͑Tṽ n ͒, P / ͑cṽ n ͒, and ṽ s / ͑ṽ n ͒ calculated from Eqs. ͑24͒-͑26͒, for w / c = 0.97 and T = 0.05 K, which we estimate 11,12 as the typical values in experiments. 3,4,7,8 We see that a strongly anisotropic phonon system in superfluid helium, where w Ϸ c, which can be created in experiments, 3,4,7,8 is a favorable experimental system for observing and studying the transverse mode.…”

Section: Transverse Modes In a Phonon Systemmentioning

confidence: 56%

“…12 we have shown that for the phonon pulses, the critical velocity is very close to the Landau critical velocity, which is equal to the first sound velocity c for pure phonon system. Direct experiments 3,4,7,8 show that the phonon pulse, injected into superfluid helium, moves through it with the velocity close to c. This means that the phonon pulse has a counterflow velocity w, with a value close to the Landau critical velocity c.…”

Section: Introductionmentioning

confidence: 56%

“…If the phonon system is isotropic, then T Յ 0.5 K, and if the phonon system is very anisotropic, as it is for a phonon pulse, then the phonon temperature must be Յ0.05 K. 11,12 The general relations ͑13͒-͑15͒, using Eqs. ͑16͒ and ͑17͒, can be written explicitly for a phonon system with a linear dispersion law,…”

Section: Transverse Modes In a Phonon Systemmentioning

confidence: 99%

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Transverse sound in differentially moving superfluid helium

et al. 2008

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There exists a transverse sound mode in superfluid helium, in addition to the first and second sound modes. In this mode, the velocity of the normal component oscillates in the direction perpendicular to the wave vector; hence, it is named the transverse mode. We analyze this mode at arbitrary values of the relative velocity of the normal and superfluid components. In general, temperature, pressure, and superfluid velocity also oscillate. The general relations between the amplitudes of the oscillating variables in the transverse mode are found in a general direction of the wave vector with respect to the relative velocity of the normal fluid and superfluid. We estimate the attenuation of the transverse mode in phonon pulses and discuss the possibility of detecting it experimentally.

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Section: Transverse Modes In a Phonon Systemmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 56%

Section: Transverse Modes In a Phonon Systemmentioning

confidence: 99%

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Transverse sound in differentially moving superfluid helium

et al. 2008

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“…In particular, it was shown theoretically using general relations that quasiparticle systems, with large values of w close to the sound velocity, are thermodynamically stable, 2 and that they possess unique thermodynamic properties. 4,5 These points are discussed in detail at the beginning of Sec. V.…”

Section: Introductionmentioning

confidence: 98%

Second sound in an anisotropic quasiparticle system of superfluidH4e

et al. 2009

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The phase and group velocities of second sound modes in superfluid helium are obtained for arbitrary values of the relative velocity of the normal and superfluid components. We show that the phase and group velocities of second sound, in general, depend on the angle between the wave vector and the relative velocity between the normal and superfluid components w. We have found the relationship between the amplitudes of the oscillating variables that describe second sound. In the general case, the normal fluid not only has a velocity component parallel to the wave vector, but also a transverse velocity component. The general expressions for the velocities and amplitudes are analyzed when the normal fluid is only due to phonons. We find that there is a certain value of w which makes the second-sound wave stationary in the laboratory frame. We show that the amplitude of the temperature oscillation, in a second-sound wave in an anisotropic phonon system, can be zero under some conditions.

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“…11 The pulse of low-energy phonons, or equivalently a small volume of normal fluid, moves through the superfluid with a velocity almost exactly equal to the sound velocity. 12 This is the maximum velocity that a normal fluid of only phonons can have, [13][14][15][16] and it is much higher than the usual critical velocity for a normal fluid with rotons, i.e., the Landau criti-cal velocity. The superfluid is very nearly stationary with respect to the experimental cell.…”

Section: Introductionmentioning

confidence: 96%

Creation of high-energy phonons in superfluidH4eand the dependence of their angular distribution on heater size

Smith

Wyatt

2010

Phys. Rev. B

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The angular distributions of high-energy phonons, that are created by a short pulse of low-energy phonons propagating in superfluid 4 He, are measured for different heater sizes and heater powers. We find that the intrinsic full width at half height of the high-energy phonons is proportional to the reciprocal of the width of the heater that creates the low-energy phonons. This is similar to the behavior shown by the low-energy phonons where the width of the phonon sheet is inversely proportional to the heater width. We discuss the correspondence between the formation of the phonon sheet by the low-energy phonons and the creation of high-energy phonons, and conclude that the phonon sheet is caused by the creation of high-energy phonons within a few millimeters of the heater. We also show that the total energy in the high-energy phonons increases linearly with heater power, once a threshold power is reached. This indicates that the initial low-energy phonons increase in number but not energy, as the heater power is increased.

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Thermodynamics of anisotropic phonon systems in superfluid helium

Cited by 9 publications

References 17 publications

Transverse sound in differentially moving superfluid helium

Transverse sound in differentially moving superfluid helium

Second sound in an anisotropic quasiparticle system of superfluidH4e

Creation of high-energy phonons in superfluidH4eand the dependence of their angular distribution on heater size

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