Observation of a kink soliton on the surface of a liquid

When a long channel of shallow liquid is driven parametrically, there can occur a 180^∘{} kink in the phase of the fundamental cross mode of the surface. The kink is stable and localized, and is nonpropagating in the limit where the system is uniform. The weakly nonlinear theoretical description is a damped driven nonlinear Schr\"odinger equation supplemented with second harmonics. The kink is a robust state even at amplitudes where the perturbation expansion leading to this equation is unjustified.