NONLINEAR EFFECTS IN VIBRATING SMECTIC FILMS

We observe nonlinear phenomena in vibrating smectic films. In particul ar, the shapes and positions of steps present in smectic films are aff ected by film vibrations. Above a certain threshold, we observe an ins tability in the meniscus consisting of the formation of a peninsula-sh aped step. We point out that these effects are driven by a nonlinear i nertial force which is tangent to the film surface and is proportional to the local density of the film and to the gradient of the film velo city squared.