[Show abstract][Hide abstract] ABSTRACT: We analyze here the analog of the Rayleigh instability in the field of gravity for the superfluid–crystal 4He interface provided that the heavier 4He crystal phase occupies the space over the lighter superfluid phase. We find that the conditions and onset of the gravitational instability are different in kind above and below the roughening transition temperature when the crystal 4He surface is in the rough or in the smooth faceted state, respectively. In the rough state of the surface the gravitational instability is fully analogous to the classical case of the fluid–fluid interface. In contrast, in the case of the crystal faceted surface the onset of the gravitational instability is associated with surmounting some potential barrier. The potential barrier results from nonzero magnitude of the facet step energy. The size and the tilting angle of the crystal facet are also important parameters for developing the instability. The initial stage of the instability can be described as a generation of crystallization waves at the superfluid–crystal interface.
In particular, we discuss the experiments (Demaria et al. in J. Low Temp. Phys. 89:385, 1992; Tsymbalenko in Fiz. Nizk. Temp. 21:162, 1995; Tsymbalenko in Low Temp. Phys. 21:120, 1995) which may concern the gravitational instability of the superfluid-crystal 4He interface.
Full-text · Article · Jan 2011 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: At the superfluid-solid 4He interface there exist crystallization waves having much in common with gravitational-capillary waves at the interface between two normal fluids. The Rayleigh-Taylor instability is an instability of the interface which can be realized when the lighter fluid is propelling the heavier one. We investigate here the analogs of the Rayleigh-Taylor instability for the superfluid-solid 4He interface. In the case of a uniformly accelerated interface the instability occurs only for a growing solid phase when the magnitude of the acceleration exceeds some critical value independent of the surface stiffness. For the Richtmyer-Meshkov limiting case of an impulsively accelerated interface, the onset of instability does not depend on the sign of the interface acceleration. In both cases the effect of crystallization wave damping is the reduction in the perturbation growth rate of the Taylor unstable interface.
No preview · Article · Jun 2009 · Physical Review E
[Show abstract][Hide abstract] ABSTRACT: We analyze an analog of the hydrodynamic Rayleigh-Taylor instability for the liquid-solid phase interface under non-uniform growth of the solid phase. The development of the instability starts on conditions of an accelerated interface growth and if the magnitude of acceleration exceeds some critical value. The plane and spherical shapes of the interface are considered. The observation of the instability can be expected for helium crystals in the course of their abnormal fast growth. Comment: Revtex, 5 pages, 3 figures
Full-text · Article · Feb 2008 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: The kinetic-growth coefficient of 4He crystal is shown to be drastically affected by an extremely small amount of 3He impurities. Such a high sensitivity with respect to impurities is due to the retardation effects in the spatial distribution of 3He atoms in front of a moving liquid-crystal interface. The kinetic-growth coefficient strongly depends on the size and shape of a crystal. The approach considered explains the features of the crystal 4He behaviour observed experimentally with introducing 3He impurities in concentration of the order of 10−6–10−5.
[Show abstract][Hide abstract] ABSTRACT: The simplest example of fingering occurs when a heavier liquid occupies the half-space above a lighter one. The fingers of
the heavier liquid driven by gravity grow down, displacing the lighter liquid upward. The fingering of the superfluid phase
into the 4He crystal facet below its roughening transition temperature can provide us an example of macroscopic quantum nucleation phenomena.
Due to cusp-like singularity in the surface tension as a function of the facet orientation the crystal facet has a relative
stability and its fingering is accompanied by overcoming some critical nucleation barrier. The barrier height is proportional
to the square of the facet step energy and depends on a ratio of the facet size to the capillary length. At sufficiently low
temperatures the thermal activation mechanism for the interface fingering is replaced with the quantum one associated with
the penetration through the nucleation barrier.
No preview · Article · Feb 2007 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: No Heading We study the behavior of the interface between the 3He-concentrated and 3He-dilute phases of a phase-separated 3He-4He liquid mixture in the presence of superflow in the d-phase. The superflow can produce a Kelvin-Helmholtz instability in the system. Here we consider two types of the instability: (i) quantized vortex in the superfluid liquid near the superfluid-normal interface; (ii) tangential flow of the superfluid component with respect to the normal fluid in the direction parallel to the interface. In these cases the Kelvin-Helmholtz instability has a threshold due to the surface tension and acceleration of the liquid in the direction normal to the interface. The acceleration is of centrifugal origin in (i) and gravitational one in (ii). The presence of the threshold results in quite different scales of characteristics distances. The centrifugal acceleration induces a scale of the order of the core radius b of several angstroms. The acceleration of gravity yields a scale of the capillary length ? 1.3 mm. In case (i) we obtain an instability of the vortex at a critical distance Rcr = b?d/(?d - ?c). The vortex should disappear at distances smaller than Rcr. In case (ii) the interface becomes unstable provided the superfluid component flows in the direction tangential to the interface with a velocity exceeding its critical value ~6.3 cm/s. There appear ripples with the wavelength of the order of the capillary constant. The instability threshold is found to be lower than in the absence of dissipation and independent of the magnitude of dissipation.
No preview · Article · Feb 2005 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: The theory is given for the decay from a metastable liquid by a quantum mechanism involving the relaxation and high frequency properties of a medium. It is our purpose to estimate the effect of relaxation time on the quantum decay rate. The theory predicts a strong dependence of nucleation regime, rate and thermal-quantum crossover temperature on both the relaxation time and the ratio of the high frequency sound velocity to the low frequency one. The shorter the relaxation time, the smaller the quantum decay rate and thermal-quantum crossover temperature. The decay rate can display a minimum in the region of the thermal-quantum crossover. The recent experiments on cavitation in normal3 He and superfluid4 He at negative pressures are discussed. The distinction in the properties of high frequency sound mode near the spinodal and in the temperature behavior of relaxation time results in a different picture of quantum cavitation in 3He and 4He.
No preview · Article · Dec 2004 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: We develop a theory in order to describe the effect of relaxation in a condensed medium upon the quantum decay of a metastable liquid near the spinodal at low temperatures. We find that both the regime and the rate of quantum nucleation strongly depend on the relaxation time and its temperature behavior. The quantum nucleation rate slows down with the decrease of the relaxation time. We also discuss the low temperature experiments on cavitation in normal $^3$He and superfluid $^4$He at negative pressures. It is the sharp distinctions in the high frequency sound mode and in the temperature behavior of the relaxation time that make the quantum cavitation kinetics in $^3$He and $^4$He completely different in kind. Comment: 10 pages, 2 figures
[Show abstract][Hide abstract] ABSTRACT: We study the oscillation spectrum of a liquid drop in the phase-separated fluid when the interfacial dynamics of phase conversion can be described in terms of the kinetic growth coefficient. For a readily mobile interface, i.e., as the growth coefficient becomes comparable with a reciprocal of the acoustic impedance, anomalous behavior is found in the oscillation spectrum of a drop. Compared with the known case of two immiscible fluids, the high interface mobility leads to an anomalous softening of the radial drop pulsations in a two-phase suspension. The anomalous behavior takes place for the drops with size not exceeding the mean free path of excitations.
No preview · Article · Dec 2001 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: We consider a quantized vortex line parallel to the interface between the concentrated (c) and dilute (d) phases of a liquid
He mixture. The vortex produces a groove-like distortion of the interface deflected into the d-phase. As a vortex approaches the interface, the bending flexure increases, reaching a maximum of 0.65m at a critical distance of 1.3m. Closer positions become absolutely unstable. Distortion of the interface leads to strong reduction of the threshold (6.3cm/s) for the Helmholtz-Kelvin tangential instability.
No preview · Article · Nov 2000 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: The recent experiments on the phase-separation kinetics in liquid 3He–4He mixtures are discussed. The nucleus of the stable 3He-concentrated phase is assumed to be located at the core of a quantized vortex. The energy of a nucleus is analysed for sufficiently large radii as an expansion in inverse powers of radius. The fact that the 3He concentration in the 3He-dilute phase cannot exceed the value at the spinodal or λ-line is involved. The results are compared with the bulk homogeneous nucleation of the stable phase.
[Show abstract][Hide abstract] ABSTRACT: Cavitation in the liquid helium isotopes of 3He and 4He is considered. It is shown that the dissipative processes play an important role in the growth of the stable phase nucleus
in the normal liquid 3He. This leads to the lack of the quantum behavior of cavitation in this system down to 2 mK, which is in contrast to the
thermal-quantum crossover in the cavitation of the superfluid 4He at 600 mK. Below 180 mK, the dissipative 3He kinetics is of the Knudsen type. The high value (600 mK) for the transition into the quantum kinetic behavior in 4He is related to the compressibility of a liquid, which leads to a noticeable emission of sound with cavitation. The recent
experiments on quantum cavitation in the liquid helium isotopes 3He and 4He are discussed.
No preview · Article · Jan 2000 · Journal of Experimental and Theoretical Physics
[Show abstract][Hide abstract] ABSTRACT: The supersaturated superfluid3He-4He mixture in the presence of quantized vortices is considered. A specific type of the lability against the vortex core expansion arises from concentrating3He atoms onto the vortex core. This affects significantly the region of the3He concentrations at which the rate of nucleating stable3He-concentrated phase can be noticeable. The most clear case of the vortex structure is a straight-line vortex with the uniformly distributed 3He atoms along the core. Such lability leads to some features in the thermal activation and quantum tunneling nucleation, resulting, in particular, in a relatively small supersaturation of about 1% which can be achieved. The critical value of the supersaturations corresponding to the vortex lability is dispersed because of the finite size of the3He-concentrated phase along the vortex core. We analyze this dispersion and its effect on the quantum separation in supersaturated3He-4He mixtures. The value of the supersaturation conserves its order of the magnitude, changing only by a numerical factor. We also emphasize an important difference of the coefficient in the term responsible for the lability from the superfluid density ?s. The supersaturation observed in experiments lies within the range of the vortex lability and, probably, is connected with this lability.
No preview · Article · Dec 1998 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: The nucleation of the
He-concentrated phase is analyzed at the phase-separation of a supersaturated liquid
He mixture in a wide range of temperatures. The crossover from the classical kinetics to the quantum kinetics is considered. Besides the homogeneous bulk nucleation the nucleation under heterogeneous conditions due to the possible presence of quantized vortices is examined.
No preview · Article · Dec 1997 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: The rate of the quantum cavitation in normal fluid 3He and superfluid 4He at temperatures down to absolute zero has been studied. The effect of energy dissipation due to viscosity and the effect of the finite compressibility of a fluid are incorporated into the calculation of the quantum cavitation rate. Because of the dissipative processes, the kinetics of the quantum cavitation in 3He and 4He proves to be qualitatively different. In normal 3He it corresponds to the dissipative tunneling through a potential barrier. In contrast, in superfluid 4He the effect of dissipation is of minor importance. In both liquids the role of the compressibility of a fluid enhances significantly for the small critical nuclei, which have several interatomic distances and can provide us the nucleation rates sufficient for the experimental observation of the homogeneous cavitation in the quantum regime.
No preview · Article · May 1997 · Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: We discuss the behavior of an extreme type-II superconductor in the magnetic field. In the very close vicinity of the upper critical fieldB
c2 the electron spectrum is gapless and the de Haas—van Alphen effect reveals the resemblance with that of metals in the normal
state, the oscillation frequency being proportional to the inverse magnetic field 1/B. The electron spectrum has a logarithmic singularity at the value of the superconducting gap δ=0. As the magnetic field decreases,
the structure of the electron spectrum changes drastically. The electron spectrum proves to be independent of the magnetic
field with the exception of the narrow region near the energies of about δ. This dependence results in the novel frequency
of magnetization oscilations, being proportional toB
No preview · Article · Jan 1996 · Czechoslovak Journal of Physics
[Show abstract][Hide abstract] ABSTRACT: We discuss the rate at which the bubbles can nucleate via quantum fluctuations in the normal3He and superfluid4He at negative pressures and sufficiently low temperatures. Unlike all the previous studies, the energy dissipation due to
the viscosity and the sound emission due to the compressibility of a fluid are involved into the bubble growth kinetics. Owing
to viscosity the quantum cavitation kinetics in3He differs qualitatively from that in4He and corresponds to the dissipative tunneling in the overdamped regime. The involvement of the compressibility results in
increasing the cavitation rate and is essential in both liquids, especially for the small critical bubbles responsible for
the experimentally observable rates of the quantum cavitation.
No preview · Article · Dec 1995 · Czechoslovak Journal of Physics
[Show abstract][Hide abstract] ABSTRACT: In extreme type-II superconductors subjected to an external magnetic field the magnetic quantum levels due to the electron orbital motion are shown to arise with the energy smaller than the magnitude of the superconducting gap. For the region of magnetic fields satisfying B2 < B < Bc2 and B2 = beta(T)Bc2 these levels cross the Fermi level, beta(T) being the known function of temperature and beta(T) < 1. Like normal metals, the presence of such levels gives rise to various oscillation and resonance effects and, in particular, to the dHvA effect in type-II superconductors.
No preview · Article · Dec 1994 · Physica C Superconductivity
[Show abstract][Hide abstract] ABSTRACT: We study the quantum two-dimensional nucleation of a stable solid phase during the first-order transition at temperatures down to absolute zero. The key role of the finite compressibility of a metastable liquid phase in calculating the quantum nucleation rate is emphasized. In particular, the nucleation rate proves to be dependent on temperature in the quantum tunneling regime. On the whole, the nucleation kinetics corresponds to dissipative tunnelung through a potential barrier. Energy dissipation is due to emitting sound waves during the growth of a solid nucleus. The features inherent to the quantum 2D growth of steps on the atomically smooth facets of a helium crystal are discussed as well.
No preview · Article · Jul 1994 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: We discuss the small He3-impurity effect on the kinetic growth coefficient of solid-liquid He4 interface. In the presence of He3 impurity, in contrast with pure He4, there arises a new additional mechanism of energy dissipation due to the He3 diffusion processes during the interface growth, resulting in a drastic decrease of the growth coefficient. Such a strong sensitivity to a very small He3 amount accounts for the anomalies observed in crystal He4 growth experiments with adding 1-10ppm of He3.
No preview · Article · Feb 1994 · Physica B Condensed Matter