Anisotropic diffusion in square lattice potentials: giant enhancement and control


The unbiased thermal diffusion of an overdamped Brownian particle in a square lattice potential is considered in the presence of an externally applied ac driving. The resulting diffusion matrix exhibits two orthogonal eigenvectors with eigenvalues D1>D2>0D_1>D_2>0, indicating anisotropic diffusion along a "fast" and a "slow principal axis". For sufficiently small temperatures, D1D_1 may become arbitrarily large and at the same time D2D_2 arbitrarily small. The principal diffusion axis can be made to point into (almost) any direction by varying either the driving amplitude or the coupling of the particle to the potential, without changing any other property of the system or the driving.Comment: 7 pages, 7 figure

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