Large amplitude local density fluctuations in a thin superfluid 4He film is considered. It is shown that these large amplitude fluctuations travel and behave like "quasi-solitons" under collision, even when the full nonlinearity arising from the Van der Waals potential is taken into account.
J. Sreekumar and Dr. V . M. Nandakumaran, “Two dimensional large amplitude quasi solitons in thin helium films”, Modern Physics Letters B, vol. 4, pp. 47–51, 1990.