Thin helium film on a glass substrate

We investigate by Monte Carlo simulations the structure, energetics and superfluid properties of thin helium-four films (up to four layers) on a glass substrate, at low temperature. The first adsorbed layer is found to be solid and "inert", i.e., atoms are localized and do not participate to quantum exchanges. Additional layers are liquid, with no clear layer separation above the second one. It is found that a single helium-three impurity resides on the outmost layer, not significantly further away from the substrate than helium-four atoms on the same layer.Comment: Six figures, submitted for publication to the Journal of Low Temperature Physic

Variational Calculations for 3^3He Impurities on 4^4He Droplets

Variational Monte Carlo method is used to calculate ground state properties of $^4$He droplets, containing 70, 112, 168, 240, 330, and 728 particles. The resulting particle and kinetic energy densities are used as an input in the Feynman-Lekner theory for $^3$He impurities. The kinetic energy density of $^4$He atoms and the energy of the $^3$He surface states are compared with the results of previous phenomenological calculations.Comment: 12 pages, in revtex 3.0, with 5 .ps figure

From nonwetting to prewetting: the asymptotic behavior of 4He drops on alkali substrates

We investigate the spreading of 4He droplets on alkali surfaces at zero temperature, within the frame of Finite Range Density Functional theory. The equilibrium configurations of several 4He_N clusters and their asymptotic trend with increasing particle number N, which can be traced to the wetting behavior of the quantum fluid, are examined for nanoscopic droplets. We discuss the size effects, inferring that the asymptotic properties of large droplets correspond to those of the prewetting film

Probing helium interfaces with light scattering : from fluid mechanics to statistical physics

We have investigated the formation of helium droplets in two physical situations. In the first one, droplets are atomised from superfluid or normal liquid by a fast helium vapour flow. In the second, droplets of normal liquid are formed inside porous glasses during the process of helium condensation. The context, aims, and results of these experiments are reviewed, with focus on the specificity of light scattering by helium. In particular, we discuss how, for different reasons, the closeness to unity of the index of refraction of helium allows in both cases to minimise the problem of multiple scattering and obtain results which it would not be possible to get using other fluids.Comment: 21 page

QUASIPARTICLE THEORY OF THE SURFACE TENSION OF LIQUID 3He AND DILUTE SOLUTION OF 4He IN 3He+

Une théorie du type quasiparticule est donnée pour la tension superficielle du liquide 3He pur et pour des mélanges dilués de 4He dans 3He. Seuls des systèmes non-superfluides sont considérés. En utilisant l'approximation des longueurs de diffusion pour des déphasages à la surface, des comparaisons entre théorie et expérience donnent une longueur ~ 3 Å pour les quasiparticules à la surface libre. Le signe de la longueur indique que les quasiparticules sont repoussées de la surface.A quasiparticle theory of the free surface tensions of pure liquid 3He and dilute solutions of 4He in 3He is given. Only normal, i.e., non-superfluid, systems are considered. Within the scattering length approximation for quasiparticle phase shifts at the surface, comparison of theory with experiment yields a length ~3 Å for 4He quasiparticles at the 3He free surface. The sign of the length indicates that the 4He quasiparticles are repelled from the surface