SURFACE-INDUCED GIANT ANISOTROPY IN THE ORDER-PARAMETER RELAXATION ATCU3AU(001)

We present a novel surface phenomenon found in the investigation of th e ordering kinetics near the surface of Cu3Au(001). Monitoring differe nt classes of Fourier components of the ordered L1(2) structure by tim e-resolved x-ray scattering, we found a giant anisotropy in the relaxa tion behavior. The layered structure normal to the surface relaxes ult rafast while lateral ordering occurs much more slowly (tau(perpendicul ar to)(-1) > 20 tau(parallel to)(-1)). We argue that the recently disc overed oscillating segregation profile acts as a two-dimensional nucle ating sheet for ordering wave vectors normal to the surface.