Competition between attractive and repulsive interactions in twocomponent BEC trapped in an optical lattice

We consider e ects of interspecies attraction on twocomponent gap solitons in thff e binary BEC with intraspecies repulsion, trapped in the onedimensional optical lattice. Systematic simulations of the coupled GrossPitaevskii equations corroborate an assumption that, because the effective mass of solitons is negative, the interspecies attraction may split the twocomponent soliton. Two critical values of the lattice strength are identified. Twospecies gap solitons are stable in strong lattices. In an intermediate region the soliton splits into a doublehumped state with separated components. Finally, in weak lattices, the splitting generates a pair of freely moving singlespecies solitons.