Interaction of microwaves with superfluid flow in HeII

Rybalko, A. S.; Rubets, S. P.; Rudavskiı̆, É. Ya.; Tikhii, V. A.; Golovashchenko, R. V.; Деркач, В. Н.; Tarapov, S. I.

doi:10.1063/1.2911649

Cited by 28 publications

(42 citation statements)

References 13 publications

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“…The recent enhanced interest in the electrical properties of helium has been triggered by a series of experimental papers [14][15][16][17][18][19][20] in which an unexpectedly high electrical activity of superfluid helium was observed when forces of a nonelectrical nature act on a system. It has been reported 14 that the propagation of second sound is accompanied by oscillations in the potential difference between two electrodes.…”

Section: Introductionmentioning

confidence: 99%

On the possibility of two phase transitions in liquid helium

Poluektov

Rybalko

2013

Low Temperature Physics

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Free energy surface of ST2 water near the liquid-liquid phase transitionAn explanation is proposed for the maxima in the dielectric constant and density observed in liquid helium slightly above the superfluid transition temperature. It is shown that they may be caused by a phase transition that results in spontaneous polarization of the helium. This kind of transition is possible in the liquid because when an atom is polarized its energy levels are lowered, so that the polarization is energetically favorable, especially for light atoms. In addition, the development of a dipole moment in an atom leads to the appearance of an additional electric field and, therefore, to an increase in the energy. The possible spontaneous polarization of the system of atoms is determined by the competition among these factors. In accordance with this concept, as the temperature of liquid helium is lowered there is an initial phase transition into a polarized normal phase, followed by one from this nonzero polarization state into the superfluid state. The transition of the normal fluid into the polarized phase is described in terms of a phenomenological theory of phase transitions. The transition can be of first or second order. V C 2013 AIP Publishing LLC.

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Section: Introductionmentioning

confidence: 99%

On the possibility of two phase transitions in liquid helium

Poluektov

Rybalko

2013

Low Temperature Physics

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“…The distance between them increases ∼ E 0 [17]. In [18,19], the authors advanced the idea of the relation of the effect to a possible quadrupole or instantaneous dipole, respectively, moment of a p-roton.…”

Section: Stark Effectmentioning

confidence: 99%

Theory of a supernarrow roton absorption line in the spectrum of a disk-shaped microwave resonator

Локтев

Tomchenko

2010

Phys. Rev. B

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We calculate the probability of the creation of a circular phonon (c-phonon) in He II by a cphoton of the resonator. It is shown that this probability has sharp maxima at frequencies, where the effective group velocity of the c-phonon is equal to zero; the density of states of c-phonons strongly grows at such frequencies. For He II, these frequencies correspond to a roton and a maxon. From the probability of the c-roton creation, we calculate the roton line width which is found to approximately agree with the experimental one. We conclude that the roton line observed in the super-high-frequency (SHF) absorption spectrum of helium is related to the creation of c-rotons. A possible interpretation of the Stark effect observed for the roton line is also proposed. Keywords: liquid 4 He, microwave resonator, circular roton, supernarrow absorption line. I. INRODUCTIONIn the recent works [1,2], an unconventional effect was discovered. In a dielectric disk-shaped resonator placed in liquid 4 He, the azimuth (l-)modes were excited. These modes are of the "whispering-gallery" type and represent a superposition of standing and running resonance electromagnetic (EM) waves of the SHF range in a narrow frequency interval. At the roton frequency ν rot = ∆ rot /2π = 180.3 GHz, the supernarrow absorption line with the width △ν ≃ 50 kHz was observed in the SHF spectrum of the resonator. This width is by six orders less than that of a roton peak measured in neutron experiments and is comparable with the width of line in the Mössbauer effect. It was assumed in [2] that the line is related to the Van Hove singularity caused by a high density of states of plane (p-) rotons near the roton minimum of the dispersion curve. In this case, however, one is faced with the problem to satisfy the momentum conservation law, since the p-roton momentum is greater than the momentum of a p-photon with the same energy by six orders. Therefore, it was supposed [2] that the excess momentum of a p-roton is transferred to helium as a whole.To clarify this and other points, it is necessary to calculate the probability of the creation of a roton and the widths and the forms of lines for various possible processes, and then to choose a process explaining the experiment. It is necessary to take into account that the EM field of a disk-shaped resonator has the circular (c-) symmetry and is concentrated only near the disk according to measurements [1] and the theory [3]. Since namely * Electronic address: vloktev@bitp.kiev.ua † Electronic address: mtomchenko@bitp.kiev.ua the EM field induces the transition, the latter must be characterized by the c-symmetry. In [3], it was shown that a phonon near a disk possesses also the c-symmetry. Therefore, we assume that the narrow line corresponds to the creation of a c-roton by the EM field of the resonator. Below, we will find the probability of this process and the width of the corresponding absorption line. A number of results required for calculations was obtained in [3]; formulas (N) from that work will be denoted...

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“…Thus, the both dynamical variables are integrals of motion for fieldfree problem which means conservation both of the total angular momentum and its z-projection on an arbitrary quantization axis. (6). This property will be used below for classification of the twoelectron shell states.…”

Section: Statement Of the Problemmentioning

confidence: 99%

“…Unusual response of superfluid helium under external electromagnetic exposure is a subject of intensive discussions over last decade [1][2][3][4][5][6][7][8]. The most impressive thing is detection of a certain low-frequency mode of 180.3  GHz which behaves like specific eigenstate of superfluid flow in 4 He [7,8].…”

Section: Introductionmentioning

confidence: 99%

“…Lower state is doubly degenerated, but in reality it is slightly splitted and the distance between upper and lower sublevels is higher due to spin-orbital interaction [50]. Three wave functions, (4) (6) , Ψ Ψ and (8) Ψ , are presented in Appendix 4. No more comparisons with experimental spectroscopic data could be made because the used basis is restricted by only single-particle states with , = 1, 2 a b n n .…”

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Helium atom in an external electric field: Exact diagonalization

Antsygina

Chishko

2014

Low Temperature Physics

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An exact diagonalization method is applied to solve the quantum-mechanical problem of spinless helium atom in an external electric field of arbitrary magnitude. The basis set for two-electron problem is built from different pair combinations ψ nalama (αr a )ψ nblbmb (αr b ) of orthonormalized single-particle hydrogen-like wave functions ψ nml (r) belonging to any possibly bound states of the individual a-and b-electrons in the Coulomb central field renormalized by the scale parameter α > 0. Within the selected basis the matrix elements of the total Hamiltonian allows an exact analytical representation in the form of finite numerical sums. The diagonalization procedure is performed by Jacobi algorithm for N×N square Hermitian matrix built on the basis of dimension N = 25. The systematics and the numerical values of the low-lying energy levels at zero field are in good agreement with known experimental data. The field dependences of low-lying levels (Stark effect) and polarizability in the ground state of helium atom are presented. It is shown that even extremely high external fields lead only to shifting or splitting of existing low levels, without disturbance of their systematics. Typically, no new lowenergy excitation can be created under external electric field of moderate intensity. Radical reconstruction in spectrum of individual helium atoms can be expected in condensed helium phases where each atom is deeply affected by interaction fields from neighbors. This result should be taken into account at interpretation of electrodynamic experiments on superfluid helium. PACS: 31.15.ac High-precision calculations for few-electron (or few-body) atomic systems.

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Interaction of microwaves with superfluid flow in HeII

Cited by 28 publications

References 13 publications

On the possibility of two phase transitions in liquid helium

On the possibility of two phase transitions in liquid helium

Theory of a supernarrow roton absorption line in the spectrum of a disk-shaped microwave resonator

Helium atom in an external electric field: Exact diagonalization

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