Wave-function monopoles in Bose-Einstein condensates

Experimental preparation of multispecies Bose-Einstein condensates should permit the creation of topologically stable defects beyond the superfluid vortex. But the coldness and isolation of condensates should also permit the survival for observable durations of "pseudodefects," such as the one-dimensional dark soliton: localized structures related to a defect but not topologically stable. In this paper we investigate the viability of pseudodefects beyond one dimension, by examining ''wave-function monopoles'' in two-species condensates in two dimensions. We identify interesting instabilities, including a "dancing mode" for monopoles of higher winding umber, and (in a one-dimensional limit) "superfluid roulette." [S1050-2947(99)51510-2].