Pseudo-contact angle due to superfluid vortices in 4He

We have investigated spreading of superfluid 4He on top of polished MgF2 and evaporated SiO2 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.