Domain Walls of Single-Component Bose-Einstein Condensates in External Potentials

We demonstrate the possibility of creating domain walls described by a single component Gross-Pitaevskii equation with attractive interaction, in the presence of an optical-lattice potential. While it is found that the extended domain wall is unstable, we show that the external magnetic trap can stabilize it. Stable solutions include twisted domain walls, as well as asymmetric solitons. The results also apply to spatial solitons in planar waveguides with transverse modulation of the refractive index.