  Interface properties of a three-component Bose-Einstein condensate, in which
component 3 is sandwiched by components 1 and 2 at the interface, are
investigated. It is shown that component 3 can serve as a surfactant: the net
interfacial tension is reduced by the presence of component 3. We calculate the
interfacial tension as a function of the interaction coefficients. The
stability of the interface is studied by Bogoliubov analysis. When the
interfacial tension has a spatial gradient, interfacial flow is induced, which
resembles the Marangoni flow.
