Novel surface modes in spinodal decomposition

We study the spontaneous phase separation of a binary mixture in the presence of a flat wall, focusing on the early stage of the demixing kinetics. Based on a Ginzburg-Landau type approach, we show the existence of novel unstable concentration waves with wave vectors (k) over right arrow(parallel to) parallel to the wall, which are characterized by a surface dispersion relation omega(s)(k(parallel to)) and amplitudes (s) over bar decaying exponentially into the bulk. The surface modes are superimposed on the laterally averaged concentration profile and are directly observable by experiment, if the wall right after a quench does not favor any of the two components of the mixture.