Dark solitons in purely quintic nonlinear lattices with defects

We demonstrate that two types of dark soliton families can be sustained in purely quintic nonlinear lattices with defects, namely on-site and off-site solitons. These solitons are classified based on whether their centers are located at lattice defects (on-site) or away from them (off-site). We analyze dark solitons in nonlinear lattices, where the lattice and defects are imprinted on an intensity background. Notably, the stability domains of off-site dark solitons are significantly larger than those of on-site solitons. In this work, we study the off-site dark solitons interacting with both short and long defects. Additionally, we investigate solitons in lattices containing one or two defects, either short or long. The stability domains of both on-site and off-site dark solitons are determined by the linear stability analysis and verified by numerical simulations.