Leonid B. Dubovskii

Diffusion mechanism in the quantum decay of metastable3He-4He mixtures at low temperatures

We study the quantum phase-separation kinetics of a supersaturated liquid mixture at temperatures down to absolute zero. The energy dissipation effect of diffusion is incorporated into the calculation of the nucleation rate in normal and superfluid liquid mixtures. Unlike single-component systems, diffusion is the principal process which governs both the quantum nucleation rate and supercritical droplet growth rate in mixtures near the demixing curve. The low temperature phase-separation experiments in supersaturated liquid3He-4He mixtures of3He-dilute phase are analyzed and discussed. The critical degree of metastability and at the same time the critical droplet radius are shown to be temperature-independent below about 80 mK, suggesting the temperature of the thermal-to-quantum crossover to be of the same order of magnitude. The critical radius of a demixed droplet is estimated as about 20 Å, being within reasonable values.

Rayleigh-Taylor instability of crystallization waves at the superfluid-solid 4He interface.

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.

On the structure of quantized vortices in a saturated liquid 3He–4He mixture

Abstract The recent experiments on the phase-separation kinetics in liquid 3 He– 4 He mixtures are discussed. The nucleus of the stable 3 He-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 3 He concentration in the 3 He-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.

Experimental and Theoretical Problems of the Quantum Phase-Separation Kinetics of Liquid 3He-4He Mixtures

The nucleation of the3He-concentrated phase is analyzed at the phase-separation of a supersaturated liquid3He–4He 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.

On the electron spectrum of a type-II superconductor in magnetic field. The magnetization oscillations

We discuss the behavior of an extreme type-II superconductor in the magnetic field. In the very close vicinity of the upper critical fieldBc2 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−1/2

De Haas-van Alphen effect in a type-II superconductor

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 = β(T)Bc2 these levels cross the Fermi level, β(T) being the known function of temperature and β(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.

Compressibility effect on the quantum two-dimensional nucleation at low temperatures

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.

Hydrodynamic instability during non-uniform growth of a helium crystal

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 acceleration exceeds some critical value. The plane and spherical shapes of the interface are considered. The observation of the instability is expected for helium crystals during their abnormal fast growth.

Vibrational spectrum of a liquid drop in phase-separated 3He-4He with a highly mobile interface

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.

Quantized Vortices Beside the Superfluid-Normal Interface

We consider a quantized vortex line parallel to the interface between the concentrated (c) and dilute (d) phases of a liquid 3He-4He 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 0.65μm at a critical distance of 1.3μm. 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.