ON THE REDUCTION OF THE CRITICAL VELOCITY IN A MODEL OF A SUPERFLUID BOSE-GAS WITH BOUNDARY INTERACTIONS

The existence of superfluidity in a 3D Bose-gas can depend on boundary interactions with channel walls. We study a simple model where the di lute moving Bose-gas interacts with the walls via hard-core repulsion. Special boundary excitations are introduced, and their excitation spe ctrum is calculated within a semiclassical approximation. It turns out that the state of the moving Bose-gas is unstable with respect to the creation of these boundary excitations in the system gas + walls, i.e . the critical velocity vanishes in the semiclassical (Bogoliubov) app roximation. We discuss how a condensate wave function, the boundary ex citation spectrum and, hence, the value of the critical velocity can c hange in more realistic models, in which ''smooth'' attractive interac tion between the gas and walls is taken into account. (C) 1998 Elsevie r Science B.V.