A new circulation condition which appears as a generalization of Mermin-Ho
relation is presented for two-component spin-1/2 Bose-Einstein condensates
as a topological constrain of the superfluid velocity due to SU(2) symmetry
of the internal states. The possibility of creating fractional vortices in
the condensate is discussed. (C) 2001 Elsevier Science B.V. All rights res
erved.