Resonant response in nonequilibrium steady states

Abstract

The time-dependent probability density function of the order parameter of a system evolving toward a stationary state exhibits an oscillatory behavior if the eigenvalues of the corresponding evolution operator are complex. The frequencies ωn, with which the system reaches its stationary state, correspond to the imaginary part of such eigenvalues. If the system (at the stationary state) is further driven by a small and oscillating perturbation with a given frequency ω, we formally prove that the linear response to the probability density function is enhanced when ω=ωn for n∈N. We prove that the occurrence of this phenomenon is characteristic of systems that are in a nonequilibrium stationary state. In particular, we obtain an explicit formula for the frequency-dependent mobility in terms of the relaxation to the stationary state of the (unperturbed) probability current. We test all these predictions by means of numerical simulations considering an ensemble of noninteracting overdamped particles on a tilted periodic potential.