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

Abstract

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.

10 pages, 4 figures