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  • 1
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the variational density matrix method, we obtain a temperature-dependent elementary excitation spectrum for two-dimensional liquid4He. For more precise results, we use a Jastrow-Feenberg-type trial wave function and include the contribution of elementary diagrams within the hypernetted chain approximation. The behavior of the excitation spectrum as a function of the temperature and density in two dimensions is similar to that of the bulk system, but has a smaller roton minimum. The roton minimum of the excitation spectrum decreases with increasing temperature and increases with increasing density at low densities but decreases at large densities. The results agree well with Monte Carlo calculations and are closer than pevious theories to experimental measurements of4He film adsorbed on substrates.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 112 (1998), S. 399-417 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using a variational Jastrow wavefunction extended to include a three-body correlation function and a hypernetted chain (HNC) and Fermi hypernetted chain (FHNC) scheme with contribution from elementary diagrams, we analyze ground-state energies and structural properties of two-dimensional 3 He- 4 He mixtures. The mixtures are in equilibrium at lower density compared to a pure 4 He system because of the large zero-point energy and statistical correlations due to the fermionic nature of 3 He. We evaluate the lowering of ground-state energies as a function of the impurity concentration and total density of mixtures. Comparing the results with boson 3 He- 4 He mixtures, we evaluate the energy shifts coming from the statistics and analyze the enthalpy to study the miscibility and mobility of each component of the mixture.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 94 (1994), S. 145-160 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Starting with the Boltzmann transport equation, the first viscosity of dilute3He-4He mixtures for various3He concentrations x is evaluated up to around T ≅ 0.6 K by including the contribution from three-phonon processes (3PP) in the anomalous elementary excitation spectrum of liquid4He. Due to 3PP, the characteristic time τη for3He viscosity at high temperatures, i.e., T⩾2TF where TF is the3He Fermi temperature, is evaluated as 5 × 10−12/xT, which is smaller than the value estimated by Rosenbaum et al. This is interpolated with τη in the degenerate (quantum) region, T≪TF. The obtained viscosities are in better agreement with experimental results than those of Baym and Saam, whose theory does not include 3PP. However, at very low concentrations there exists a discrepancy between the present theory and experiments, so that an alternate treatment should be considered.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 85 (1991), S. 331-346 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the results of ground-state energies, radial distribution functions, liquid structure functions and effective interactions for a3He impurity in a4He background in two dimensions. The hypernetted-chain scheme for the system described by a Jastrow-type wavefunction is used, taking into account the triplet correlations and elementary diagrams up to fifth order. Solving the Euler-Lagrange equations for the two-body distribution functions, which contain triplet correlation and elementary diagrams, improves the results considerably. Furthermore, as a3He impurity is inserted into the4He background, the ground-state energy increases, but the equilibrium density decreases from 0.0350 Å−2 to 0.0336 Å−2. The radial distribution function is broadened, while its maximum is lowered and shifted to the right (the direction of increasing radial distance) due to its larger zero-point energy, with therefore less localization of the3He particle. The results are compared with Monte Carlo results and other studies.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 78 (1990), S. 51-61 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Temperature variations of the quasi-diffusion constant and thermal diffusion ratio between phonon and roton gases in two- and three-dimensional liquid helium are evaluated explicitly through the scattering of phonons by rotons. The diffusion constants in both dimensions decrease exponentially over the whole temperature range, while the thermal diffusion ratios increase and then decrease as temperature increases in the range from ∼0.6 to ∼1.1 K.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 95 (1994), S. 547-578 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The temperature variations of the diffusion coefficientD(T), thermal diffusion ratio k T (T) and thermal conductivity κ(T) in a dilute solution of3He atom in two-dimensional liquid helium are evaluated explicitly by solving the kinetic equations via phonon-phonon, phonon-roton, roton-roton, impurityelementary excitation and impurity-impurity scatterings. In the low-temperature region, the main contributions toD(T) and κ(T) come from the interactions between phonons and impurities, while in the high-temperature region the interactions between impurities and whole elementary excitations contribute more strongly toD(T) and κ(T) than those of only elementary excitations. For a dilute solution, the thermal diffusion ratio k T (T), neglecting the internal mass counterflow, is much smaller than the effective thermal diffusion ratio k T * (T), which is a function of thermostatic properties. The effective thermal conductivity κeff is much larger than the thermal conductivity and has different temperature dependence from the thermal conductivity. The behaviors of the two-dimensional diffusion coefficient and thermal conductivity are much like the bulk case, where they exhibit exponential decay with increasing temperature, although they are much smaller than those of the bulk case.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of Russian laser research 12 (1991), S. 385-394 
    ISSN: 1573-8760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 109 (1997), S. 495-510 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effects of three-phonon processes on the phonon thermal conductivity and phonon viscosity in dilute 3He-4He mixtures below 0.6 K are investigated. The characteristic scattering times for phonon-phonon interaction-limited thermal conductivity and viscosity are calculated from a collision matrix which contains information on the three-phonon processes. We find that due to phonon-3He interactions the phonon momentum range in which three-phonon processes occur is reduced in comparison with that of the pure 4He case. Results for thermal conductivity and viscosity show good agreement with experimental data without having to adjust the rates of phonon absorption by 3He and the rates of elastic scattering of phonons with 3He.
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  • 9
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We calculate the ground-state energies and the radial distribution functions of two-dimensional quantum fluid4He, mass 3 boson3He and3He within a hypernetted chain and a Fermi hypernetted chain summation method. To get more accurate results, we include three-body correlation functions in the trial wavefunctions and consider the contributions arising from elementary diagrams via scaling approximations. The two-dimensional4He system has a binding energy of 0.84 K at an equilibrium density 0.042 Å−2, which is closer to the result of a Green's function Monte Carlo calculation than previous ones, while mass 3 boson3He has 0.286 K at 0.025 Å−2. The3He system is not self-bound and therefore not a liquid state due to its statistics and light mass of the3He atom. We calculate the ground-state energy of two-dimensional liquid4He through a Lennard-Jones potential and that of Aziz to compare the results of both. Aziz's potential gives lower and more accurate energies than the Lennard-Jones potential, as in three dimensions.
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  • 10
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Starting from the system of linearized kinetic equations, the exact expressions for the spin and mass diffusion coefficients and thermal diffusion ratio in quantum mixtures of helium isotopes with any degree of degeneration is obtained. From the general expression the various limiting expressions have been obtained, which are determined by various relations between collision rates of quasiparticles. The results of the calculations are compared with available experimental data. It is shown that in the low-temperature region, where an impuriton gas is one-component, the relaxation of concentration of 3 He in superfluid 3 He– 4 He mixtures is determined by the acoustic and dissipative collective modes with an effective diffusion coefficient. From the general relation, the expression for a spin diffusion coefficient in solid 3 He– 4 He quantum mixtures is derived. The comparison of the results obtained with the experimental data makes it possible to find a numerical value for the width of the impuriton energy zone.
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