Experimental Evidence for an Interface Delocalization Transition in Cu3Au\mathrm{Cu_3Au}

The Cu$_3$Au(100) surface has been studied close to the bulk order-disorder transition temperature T$_0$ by x-ray diffraction under total external reflection. The order-parameter profile which has been probed in various depths is analyzed in terms of a surface-induced disorder transition. It is demonstrated that the temperature dependence of the superlattice intensity is consistent with the assumption of a disordered surface layer which exists between the ordered bulk and the vacuum at temperatures below T0 and grows logarithmically as T$_0$ is approached