Anisotropic diffusion in stress fields

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Abstract
The effects of external fields on the diffusion of particles in crystals is discussed. Emphasis is put on the anisotropy of drift diffusion due to elastic strain fields in cubic crystals. The continuum equation of diffusion is derived microscopically from lattice theory. It is shown that in an elastic strain field the anisotropy of the saddle-point configuration leads to an anisotropic diffusion, whereas the possible anisotropy of the equilibrium configuration is unimportant. In an homogeneous strain field the diffusion is characterized by three independent "elasto-diffusion constants," the measurements of which yield direct information about the symmetry and strength of the dipole tensor of the saddle-point configuration. Possible applications to other problems are discussed briefly.