Domain wall dynamics in Bose-Einstein condensates with density-dependent gauge field

We investigate the formation and dynamics of domain walls in a Bose-Einstein condensate under a density-dependent gauge field. The density-dependent gauge field is created by simultaneous modulations of an optical lattice potential and interatomic interactions, and results in domains of atoms condensed into two different momenta. We observe deterministic formation of domain walls due to the density inhomogeneity of the atomic cloud. We further study the dynamics of the domain walls under a synthetic electric field. Modeling the topological defects as elementary excitations, we find that they respond to the electric field with an effective charge-to-mass ratio larger than and opposite to that of the bare atoms.