Superfluid Liquid Research Articles

Reux operators of physical variables and the method of quasiaverages

Generah expressions for the operators of the flux densities of physical quantities are obtained in terms of the density operators of the quantities in question. With the aid of the method of quasi-averages, the expressions obtained for the flux operators make it possible to find the averages of these operators in terms of the thermodynamic potential of superfluid liquid in statistical equilibrium. (auth)

Soundlike Collective Excitations in SuperfluidHe3

I discuss soundlike collective excitations in anisotropic superfluid Fermi liquids in both the collisionless and the hydrodynamic regimes. Expressions for the velocities of zero, first, second, and fourth sound are derived in terms of the Landau parameters of the normal state. The second- and fourth-sound velocities are found to vary appreciably with orientation.

Spectrum of spontaneous light scattering from a superfluid liquid surface

An expression for the spectral intensity of light scattered from the thermal fluctuations of free superfluid liquid surface is suggested.

Interaction between radiation and a superfluid liquid surface

The surface motion of a superfluid liquid due to ponderomotive effect of radiation on matter is discussed. In particular, the possibility of optical excitation of surface (capillary) waves in a superfluid liquid (He II) is considered. Under certain conditions this effect is shown to cause instability of surface waves, i.e., stimulated surface scattering of light in a superfluid liquid.

Relaxation phenomena at accelaration of rotation of a spherical vessel with helium II and relaxation in pulsars

Measurements of the rotational speed of the PSR 0833 pulsar in Vela and PSR 0531 in the Crab nebula have shown that after a sudden speed-up of their rotation a considerably long relaxation process is observed. According to Pines [1] it is associated with the neutron star's superfluidity predicted by Migdal [2]. The present paper is devoted to an attempt of modelling these processes observing the relaxation motions of liquid helium after sharp changes in the rotational speed of a spherical vessel filled with superfluid liquid.

The boson method in superconductivity: Application to the study of the Josephson effect

The boson method in superconductivity is applied to the study of the Josephson effect. This approach permits us to calculate all the important observable quantities, like the magnetic field and the current, at any point of the system, without making’ use of any phenomenological assumption, such asJ =j1 sinϕ. The results of our calculation show a qualitative agreement with those computed by other authors on the basis of the Josephson equation, though we do not have and we do not use this equation. The boson method is also able to yield results for a neutral superconductor, so that the calculations can be applied to the analogous effects that can be found in superfluid liquids. Finally, we would like to point out that our results do not necessarily satisfy the phenomenological equationJ =j1 sinϕ.

Criticism of the Single-Particle-Green's-Function Approach to the Excitation Spectrum of Superfluid Liquid Helium

Criticism of the Single-Particle-Green's-Function Approach to the Excitation Spectrum of Superfluid Liquid Helium

Evidence of Metastable Atomic and Molecular Bubble States in Electron-Bombarded Superfluid Liquid Helium

Evidence of Metastable Atomic and Molecular Bubble States in Electron-Bombarded Superfluid Liquid Helium

Evidence of Metastable Atomic and Molecular Bubble States in Electron-Bombarded Superfluid Liquid Helium

Evidence of Metastable Atomic and Molecular Bubble States in Electron-Bombarded Superfluid Liquid Helium

Quantum effects in weakly coupled superfluid liquids

The boson method is applied to the study of two superfluid liquids joined together by a weak link. A microscopic derivation of experimental results is presented.

Vortex Motions in Ideal Bose Superfluid.

A general nonlinear field equation is derived for the macroscopic order parameter of an ideal coherent Bose gas. It is shown that this noninteracting system can support stable quantized vortex-like motions within the superfluid phase. It is suggested that this coherent phase of the ideal Bose gas describes the dominant physical features of real superfluid liquid helium.

Experiments with Charged Quantized Vortex Rings in Superfluid Liquid Helium

Experiments with Charged Quantized Vortex Rings in Superfluid Liquid Helium

Ion Motion in Superfluid Liquid Helium under Pressure

Recent investigations of superfluidity by a study of the mobilities of ions in liquid He ii have been extended to the liquid under pressure. At a fixed temperature the positive-ion mobility decreases appreciably as the pressure is increased, particularly at low temperatures. At a fixed pressure the mobility increases less rapidly with decreasing temperature at higher pressures. The negative-ion mobility, smaller than that of the positive ion at zero pressure, becomes equal to that of the latter above 7 atm. In high electric fields and at high pressures, the drift velocity of the negative ions approaches a limiting value roughly equal to the Landau critical velocity for a body moving through the superfluid. The theory, which discusses the mobility in terms of ion scattering by rotons and phonons, is reviewed. It is pointed out that previously neglected effects concerned with the importance of small-angle scattering of the ion ought to be taken into account; some earlier estimates of scattering cross sections are revised accordingly. It is then shown that this theory, making use only of the known change of the roton dispersion relation with pressure, can account quantitatively for the observed pressure dependence of the positive-ion mobilities.

Hydrodynamics of liquid helium

Publisher Summary This chapter presents a brief account of the theoretical work done by L. Landau and by the authors on the hydrodynamics of the superfluid helium. The exact system of hydrodynamical equations of the superfluid liquid can be obtained quite unambiguously starting from the conditions imposed by the conservation laws, by the Galilean relativity principle, and also from certain properties of the motion, which are the consequence of the microscopic theory of superfluidity. One more equation is to be added that determines the acceleration of the superfluid motion. It is to be stressed that the unambiguous derivation of the approximate hydrodynamical equations is possible only by means of performing appropriate neglections in the exact equations. If one performs these neglections from the very beginning, then one loses the possibility of an unambiguous derivation on the basis of the conservation laws and of the relativity principle.