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We studied numerically the Andreev scattering cross-sections of three-dimensional isolated quantized vortex rings in superfluid 3He-B at ultralow temperatures. We calculated the dependence of the cross-section on the ring's size and on the angle between the beam of incident thermal quasiparticle excitations and the direction of the ring's motion. We also introduced, and investigated numerically, the cross-section averaged over all possible orientations of the vortex ring; such a cross-section may be particularly relevant for the analysis of experimental data. We also analyzed the rôle of screening effects for Andreev reflection of quasiparticles by systems of vortex rings. Using the results obtained for isolated rings we found that the screening factor for a system of unlinked rings depends strongly on the average radius of the vortex ring, and that the screening effects increase with decreasing the rings' size. [ABSTRACT FROM AUTHOR]

Spatially inhomogeneous coherently precessing structures of half magnetization in superfluid [sup 3]He-B are investigated in the presence of small nonuniformities of a high external magnetic field. It is shown that, depending on the degree of nonuniformity of the field, both two-domain and three-domain coherently precessing structures can exist. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The regimes of coherent precession of "zero" magnetization in a transverse rf field in the superfluid A phase of liquid [sup 3]He are investigated with dissipative processes taken into account. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the spatially homogeneous spin dynamics of the superfluid phases of liquid helium with dissipation for the general spin-orbital configurations. Role of a weak spin-orbital coupling stemming from the dipole-dipole interaction between nuclear magnetic moments of helium atoms; Non-Leggett orbital configuration.

New coherently precessing spin states in superfluid A and B phases of liquid3 He and antiferromagnetic U2D2 solid3 He are described. These unconventional dynamical modes are stabilized in the states with nonequilibrium value of the magnitude $${\text{M = }}\left| {\overrightarrow {\text{M}} } \right|$$ of the nuclear magnetization. Especially interesting regimes are developed at one half of the equilibrium magnetization (M = M0/2, M0 = χH0). One of such exotic dynamical modes has been recently observed in3 He-B. [ABSTRACT FROM AUTHOR]

Superfluid 3He-B in the zero-temperature limit offers a unique means of studying quantum turbulence by the Andreev reflection of quasiparticle excitations by the vortex flow fields. We validate the experimental visualization of turbulence in 3He-B by showing the relation between the vortex-line density and the Andreev reflectance of the vortex tangle in the first simulations of the Andreev reflectance by a realistic 3D vortex tangle, and comparing the results with the first experimental measurements able to probe quantum turbulence on length scales smaller than the intervortex separation. [ABSTRACT FROM AUTHOR]

Andreev reflection of thermal quasiparticles from quantized vortices is an important technique to visualize quantum turbulence in low temperature 3He-B. We revisit a problem of Andreev reflection from the isolated, rectilinear vortex line. For quasiparticle excitations whose impact parameters, defined as distances of the closest approach to the vortex core, do not exceed some arbitrary value b, we calculate exactly the reflected fraction of the total flux of excitations incident upon the vortex in the direction orthogonal to the vortex line. We then define and calculate exactly, as a function of b, the scattering length, that is the scattering cross section per unit length of the vortex line. We also define and calculate the scattering lengths for the flux of energy carried by thermal excitations, and for the net energy flux resulting from a (small) temperature gradient, and analyze the dependence of these scattering lengths on temperature. [ABSTRACT FROM AUTHOR]

The B phase of superfluid 3He can support regions of extremely long-lived coherent spin precession at ultralow temperatures, known as persistent precessing domains (PPD). The domains have been described in terms of a Bose-Einstein condensate of magnons and in terms of Q balls in field theory. The domains form in a magnetic field minimum along the vertical axis of a cylindrical cell. When far from the ends of the cell, the PPD lifetime grows exponentially on decreasing temperature. When the PPD is close to the horizontal end wall of the cell, an extra surface dissipation mechanism dominates at low temperatures. We present measurements of the PPD generated at various locations in the cell over a broad range of temperatures below 0.3 Tc- We compare the measured properties with theoretical expectations for spin-wave modes. We present model calculations of different dissipation mechanisms and we compare these to the measured lifetimes. [ABSTRACT FROM AUTHOR]

We present a combined numerical and experimental study of Andreev scattering from quantum turbulence in superfluid ³He-B at ultralow temperatures. We simulate the evolution of moderately dense, three-dimensional, quasiclassical vortex tangles and the Andreev reflection of thermal quasiparticle excitations by these tangles. This numerical simulation enables us to generate the two-dimensional map of local Andreev reflections for excitations incident on one of the faces of a cubic computational domain, and to calculate the total coefficient of Andreev reflection as a function of the vortex line density. Our numerical simulation is then compared with the experimental measurements probing quantum turbulence generated by a vibrating grid. We also address the question of whether the quasiclassical and ultraquantum regimes of quantum turbulence can be distinguished by their respective total Andreev reflectivities. We discuss the screening mechanisms which may strongly affect the total Andreev reflectivity of dense vortex tangles. Finally, we present combined numerical-experimental results for fluctuations of the Andreev reflection from a quasiclassical turbulent tangle and demonstrate that the spectral properties of the Andreev reflection reveal the nature and properties of quantum turbulence. [ABSTRACT FROM AUTHOR]