Thermal fluctuations, subcritical bifurcation, and nucleation of localized states in electroconvection

Measurements of the mean-square amplitude [theta(2)] of thermally induced fluctuations of a thin layer of the nematic liquid crystal I52 subjected to a voltage V are reported. They yield the limit of stability V-c of the spatially uniform conduction state to infinitesimal perturbations. Localized long-lived convecting structures known as worms form spontaneously from the fluctuations for V well below V-c. This, as well as measurements of the lifetime of the conduction state for V < V-c, suggests a thermally activated mechanism of worm formation.