Nonequilibrium fluctuations, effective temperature, and effective interactions driven by irradiation of alloys

We study alloy systems subjected to sustained particle irradiation, where short-ranged thermally assisted diffusion competes with the finite-ranged random atomic exchanges forced by irradiation. For the case of binary alloys undergoing phase separation, we introduce a kinetic continuum description of the evolution of the composition field under irradiation, with a self-consistent treatment of the composition fluctuations. We derive an analytical formula for the structure factor at steady state. In the limiting case of short-ranged ballistic jumps, this formula indicates that the effective temperature criterion originally derived by G. Martin [Phys. Rev. B 30, 1424 (1984)] applies not only to the driving force but to the fluctuations as well. In the case of finite-ranged ballistic jumps, however, the formula indicates that the concept of an effective temperature breaks down, but that one can make use of a more general approach involving effective atomic interactions. In particular, under appropriate irradiation conditions, finite-ranged ballistic jumps lead to finite-ranged effective interactions, which translate into the dynamical stabilization of finite-scale composition patterns.