Subsurface ordering kinetics at Cu3Au (001)

The peculiar two-step ordering kinetics, discovered recently in time-resolved X-ray experiments on the Cu3Au(001) surface after a temperature quench to the ordered phase is analyzed within the time-dependent Ginzburg-Landau theory. Our model accounts for both the fast propagation of an ordering wave into the bulk, initiated by Au-surface segregation, and a time-delayed propagation of lateral order from the bulk to the surface. We also discuss further effects predicted by our theory, like the appearance of a characteristic penetration depth of the ordering wave and a secondary relaxation in its amplitude, which have not yet been detected experimentally.