Observations of localized structures in nonlinear lattices: Domain walls and kinks.

Steady-state domain walls and kinks have been observed in one-dimensional nonlinear lattices that are damped and parametrically driven. These states are localized robust transition regions between two extended standing-wave domains of definite wave number. The observations are made in an experimental lattice of coupled pendulums and in simplified numerical models. A nonlinear Schr\"odinger theory is developed for kinks in the upper cutoff mode. There is currently no theory for the domain walls and noncutoff kinks, which are fundamentally new localized structures.