Vector gap solitons of two-component Bose gas in twisted-bilayer optical lattice

Motivated by recent experimental realization of atomic Bose–Einstein condensate in twisted-bilayer optical lattices, we consider the vector gap solitons and their stability in a two-component Bose–Einstein condensate confined in twisted-bilayer optical lattice, where the structures of the linear Bloch band-gaps are dominated by the amplitudes of sublattices. We find families of vector gap soliton in the Bloch band-gap, showing strong dependent on contact interactions. It is shown that the existence region of vector gap solitons is mainly related to attraction interaction in the semi-infinite gap, while to repulsion interaction in the first gap. For the unequal chemical potential with significant difference, the component with higher chemical potential is easier to form solitons. In regions farther or closer to the Bloch band, the shapes of such vector gap solitons are mainly determined by the chemical potential. Finally, we preform the stability analysis of such vector gap solitons by linear and nonlinear method, showing that both the attractive interaction and the position of gap solitons in the band-gap may cause solitons to be unstable.