Pseudo-contact angle due to superfluid vortices in 4^{4}He

We have investigated spreading of superfluid $^{4}$He on top of polished MgF$_2$ and evaporated SiO$_{2}$ substrates. Our results show strongly varying contact angles of 0 - 15 mrad on the evaporated layers. According to our theoretical calculations, these contact angles can be explained by a spatially varying distribution of vortex lines, the unpinning velocity of which is inversely proportional to the liquid depth.Comment: 10 pages, 4 figure

Elementary steps on the He-4 crystal interface probed by He-3 atoms

The growth dynamics of c facets, governed by individual Frank-Read type of sources, has been studied at millikelvin temperatures in the presence of small concentrations of He-3 atoms in the liquid. We find that in the spiral growth regime, interaction of He-3 atoms with moving elementary steps on the surface results in additional friction. Our results are compared with theory, where high-frequency (omega greater than or equal to T/(h) over bar) zero-point oscillations of the steps are taken into account. There is a good agreement if we assume the amplitude of these oscillations xi approximate to 5 nm