Ultrawide dark solitons in ultracold Bose systems with competing interactions

We investigate the behavior of dark solitons in two types of one-dimensional ultracold systems: dipolar bosons and Bose-Bose mixtures. In both systems, there are two types of interactions - a long-range attractive interaction and a repulsive contact interaction in the former. In the latter - attractive intercomponent and repulsive intracomponent interactions. By combining hydrodynamics and ab initio models, we extend the understanding of dark solitons beyond the Gross-Pitaevskii equation. Our equations have different types of nonlinearities, leading to novel results. Our findings show that at a critical interaction strength, the solitons broaden significantly, exhibiting an unconventional dispersion relation, and lacking the typical phase jump and zero minimum density features of stationary solitons. This behavior is universal across both dipolar atoms and mixtures. Our results also suggest that these solitons may exist within quantum droplets.