X-ray intensity fluctuation spectroscopy studies on phase-ordering systems.

The order-disorder phase transition in Cu3Au has been studied by x-ray intensity fluctuation spectroscopy. Following a quench from the high-temperature, disordered phase, the ordering kinetics is well described by a universal scaling form that can be measured by time-resolved (incoherent) x-ray scattering. By using coherent scattering, we have measured the fluctuations about this universal scaling form. In the late stages of the ordering process, these fluctuations give a two-time correlation function C(q,t1,t2) which has a scaling form with natural variables deltat=/t1-t2/ and t =(t1+t2) / 2. The scaling form crosses over from linear in t to t1/2. These present the first such results for a nonconserved system.