Superlattice patterns in vertically oscillated Rayleigh-Benard convection

We report the first observations of superlattices in thermal convection. Th e superlattices are selected by a four-mode resonance mechanism that is qua litatively different from the three-mode resonance responsible for complex- ordered patterns observed previously in other nonequilibrium systems. Numer ical simulations quantitatively describe both the pattern structure and the stability boundaries of superlattices observed in laboratory experiments. In the presence of the inversion symmetry, superlattices are found numerica lly to bifurcate supercritically directly from conduction or from a striped base state.