Nonlocal dark solitons and interactions under fourth-order diffraction

Dark solitons and interactions are investigated in nonlocal media under the condition of fourth-order diffraction (FOD). In the case of weak nonlocality or rectangular nonlocal response function, analytical solutions of dark solitons are obtained via Lagrangian (variational) method. Numerical results show that solitons are unstable (stable) when FOD is anomalous (normal). Interactions of dark soliton with FOD are described analytically with an interacting potential and confirmed by numerical simulations. With the help of attractive force originated from strong degree of nonlocality and anomalous FOD, bound states of dark solitons are generated, otherwise they are always repulsive.