Impact of cross and main diffusion coefficients on symmetry breaking in nonreactive diffusion systems

Diffusion-triggered convection can occur in a gravitationally stable system of two superimposed mixtures. As instability develops, two distinct patterns may emerge: double-diffusive (DD) or diffusion-layer convection (DLC). Traditionally, nonsymmetric patterns above and below the interface were thought to require chemical reaction. We show that symmetry can be broken by composition-dependent diffusion, with or without cross diffusion. Furthermore, only the composition-dependent cross diffusion can lead to a range of coexisting patterns and provide new insights into staircase instability.