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  • 1
    Electronic Resource
    Electronic Resource
    Vortex core size in submonolayer superfluid4He films (1995)
    Springer
    Journal of low temperature physics 101 (1995), S. 463-468 
    Details
    ISSN: 1573-7357
    Keywords: 67.40.Rp ; 67.40.Kh ; 67.40.Vs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The superfluid transition of4He films adsorbed on 500 Å diameter slip-cast alumina powder is measured with a torsion oscillator technique for films with transition temperatures between 50 and 700 mK. The transitions are found to be controlled by the universal Kosterlitz- Thouless critical line, but a strong increase in the broadening of the transition is observed for the thinnest films. Analysis in terms of vortex pair excitations shows that this broadening results from a vortex core size that increases rapidly as the film is thinned, scaling roughly with the interparticle spacing of the superfluid submonolayer. Third sound modes are identified in the dissipation, in addition to a broad peak from the vortex unbinding. This system provides evidence of a three-dimensional superfluid transition mediated by vortex excitations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00753338
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  • 2
    Electronic Resource
    Electronic Resource
    Superfluid Phase Transition of 3He-4He Mixture Films Adsorbed on Alumina Powder (1998)
    Springer
    Journal of low temperature physics 110 (1998), S. 533-538 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The superfluid phase transition of 3 He- 4 He mixture films adsorbed on 500 Å alumina powder has been studied for mixture films whose superfluid thickness is less than a monolayer. The transitions are found to be controlled by the Kosterlitz-Thouless critical line, but a strong broadening of the transition is observed as the 3 He concentration is increased. Analyzing the broadening in terms of a KT vortex-pair theory modified for the the finite powder size yields a vortex core parameter which increases nearly linearly with added 3 He. Also observed in these measurements is a temperature-dependent and 3 He-dependent depletion of the superfluid density at low temperatures, which is thought to arise from the high-frequency ripplon/third sound excitations of the film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022506816244
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  • 3
    Electronic Resource
    Electronic Resource
    Vortex-Ring Specific Heat of Superfluid Helium in Porous Materials (1998)
    Springer
    Journal of low temperature physics 110 (1998), S. 567-572 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The specific heat of superfluid 4 He in a porous material is calculated using a vortex-ring renormalization theory, both for completely filled pores and for thin films. The porous medium introduces a new length scale L into the problem which is of the order of the pore size of the material, and which becomes the starting vortex-ring size of the recursion relations (the T=0 correlation length). The specific heat displays a lambda-like critical peak, but the amplitude of the peak is suppressed by a very large factor (L/a o ) 3 compared to the bulk, where a o ≈ 2.5 Å is the starting ring size for the bulk liquid calculation. This is in agreement with scaling theories invoking “two-scale-factor universality”, and provides a simple picture of the superfluid transition in porous materials, where the vortex cores of the rings are the material itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022519218970
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  • 4
    Electronic Resource
    Electronic Resource
    Vortex Pair Energy in an Anisotropic Superfluid Film (1998)
    Springer
    Journal of low temperature physics 113 (1998), S. 405-410 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The energy and impulse of a vortex pair are calculated for a helium film in which the superfluid density is anisotropic in the plane of the film, such as might be induced by a supercurrent. Surprisingly, the energy of the pair in its rest frame is found not to depend on the angle between the anisotropy direction and the axis of the pair, but to have the same form as for an isotropic film, the only change being that the superfluid density is replaced by the geometric mean of the parallel and perpendicular components of the superfluid tensor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022535708588
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  • 5
    Electronic Resource
    Electronic Resource
    Ion trapping on vortex lines in rotating 3He-4He mixtures (1978)
    Springer
    Journal of low temperature physics 33 (1978), S. 459-480 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: The trapping lifetime and mobility of positive and negative ions on vortex lines in 3He-4He mixtures have been measured in the temperature range between 0.1 and 1.3 K. The binding energy of the positive ion is found to be reduced by the 3He, and the mobility of both ion species is lowered, providing evidence that the 3He condenses at the vortex core. The negative ion trapping lifetime is smaller than that of the positive ion in the region 0.3–0.5 K, indicating that the bubble structure may be modified by the presence of the condensed 3He. At 0.3 K the negative ion lifetime increases sharply, in qualitative agreement with theoretical models predicting an increase in the bubble radius at that temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115570
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  • 6
    Electronic Resource
    Electronic Resource
    Pressure release superleak sound modes in He II (1980)
    Springer
    Journal of low temperature physics 38 (1980), S. 629-640 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: The sound modes of He II in a waveguide partially packed with superleak are investigated for the case of a free surface within the waveguide. In the limit of zero vapor density, two propagating modes are found: one a gravity wave whose velocity depends on the superfluid fraction, and the other a temperature wave which is analogous to adiabatic U-tube osculations. With finite vapor the U-tube mode in pure 4He mixes strongly with the vapor sound; however, in 3He-4He mixtures it is uncoupled from the vapor and is observable. Experimental results are in qualitative agreement with the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115493
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  • 7
    Electronic Resource
    Electronic Resource
    Vortex dynamics at the superfluid λ-transition (1993)
    Springer
    Journal of low temperature physics 93 (1993), S. 1079-1095 
    Details
    ISSN: 1573-7357
    Keywords: 67.40 Fd ; 67.40 Vs ; 67.40 Kh ; 64.60 Ht
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A vortex-ring theory of the superfluid4He λ-transition is extended to include the dynamics of the transition. The response of the vortices to an oscillating superflow is found by solving the Fokker-Planck equation. This allows a calculation of the superfluid relaxation time, which is in agreement with Landau-Khalatnikov theory and with dynamic scaling. At high frequencies the transition becomes broadened, with both the superfluid density and the dissipation remaining finite at and above Tλ. Comparison is made to earlier theories that use high-temperature expansions and renormalization-group expansions. Applications to other subjects such as mutual friction, high-Tc superconductors, and rapidly quenched systems are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00692050
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  • 8
    Electronic Resource
    Electronic Resource
    Multiply charged droplets in helium vapor (1984)
    Springer
    Journal of low temperature physics 57 (1984), S. 539-547 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A model is introduced for the structure of multiply charged droplets occurring in low-temperature helium vapor. The regime of stability for the droplets is investigated. We find that only saturated droplets are stable with respect to angular oscillations. Experiments are suggested to probe this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683679
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  • 9
    Electronic Resource
    Electronic Resource
    A technique for photographing vortex positions in rotating superfluid helium (1980)
    Springer
    Journal of low temperature physics 39 (1980), S. 553-577 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A technique is described for photographing the positions of quantized vortex lines in rotating superfluid helium. Electron bubbles are trapped on the lines, and then extracted through the free surface and accelerated into a phosphor screen. Details of the apparatus are presented, along with examples of the data and the data collection techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00114894
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  • 10
    Electronic Resource
    Electronic Resource
    Attenuation of superfluid two-phase sound (1983)
    Springer
    Journal of low temperature physics 50 (1983), S. 455-474 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The attenuation of superfluid two-phase sound in4He is calculated and compared with experimental results. The dispersion relation of this mode (which consists of coupled vapor sound and second sound) is determined by boundary conditions at the free liquid surface. The primary source of attenuation is found to be the evaporation-condensation process at the free surface. A calculation using kinetic models for the nonequilibrium Onsager coefficients yields an attenuation in general agreement with experimental measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683490
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