Surface Diffusion Of A Brownian Particle Subjected To An External Harmonic Noise

Harmonic noise has been widely used in various physical situations,either as an internal or an external noise.Some dynamic characteristics have been obtained.As a kind of stochastic differential equation,the Langevin equation is very successful in describing the surface diffusion of a Brownian particle and other stochastic processes.Langevin simulation is performed to investigate the diffusion coefficient versus parameters for a Brownian particle moving in a two-dimensional coupled periodic potential and subjected to an external harmonic noise.A series of characteristics of diffusion coefficient are obtained by numerical simulation and the corresponding physical mechanism are revealed.Resonant diffusion phenomenon is observed as a result of the coupling between the central frequency of the spectral density of the harmonic noise and the frequency of the potential well bottom.The diffusion coefficient presents approximately linear functions of the strengths of the internal and external noises for low values of the strengths.This can be understood by the local linearization approximation of the potential force.The damping coefficient dependence of the diffusion coefficient in lower damping is well fitted by a negative power relation D ? ?-?,as an internal Gaussian white noise case does,but with a power whose absolute value is larger than 1.This can be qualitatively understood by the external noise promoting the diffusion of the Brownian particle.The surface diffusion of a Brownian particle presents jump diffusion for low values of the internal and external noises.For the case that external harmonic noise is independent in the directions of x and y,Langevin simulation indicates that surface diffusion of a Brownian particle subjected to a two-dimensional coupled periodic potential is qualitatively identical with the large values of the noises,but with some difference.The difference is that the diffusion coefficient does not presents approximately linear functions of the strengths of the internal and external noises,and the damping coefficient dependence of the diffusion coefficient deviates from the usual negative power relation.We have calculated the diffusion coefficient by the extended Kramers escape rate theory.The results are qualitatively consistent with numerical simulation.We should consider the detailed structure of the potential for quantitative comparison.