  Diffusion of particles has wide repercussions ranging from particle-based
soft matter systems to solid state systems with particular electronic
properties. Recently, in the field of magnetism, diffusion of magnetic
skyrmions, topologically stabilized quasi-particles, has been demonstrated.
Here we show that by applying a magnetic in-plane field and therefore breaking
the symmetry of the system, the skyrmion diffusion becomes anisotropic with
faster diffusion parallel to the field axis and slower diffusion perpendicular
to it. We furthermore show that the absolute value of the applied field
controls the absolute values of the diffusion coefficients so that one can
thereby uniquely tune both the orientation of the diffusion and its strength.
Based on the stochastic Thiele equation, we can explain the observed
anisotropic diffusion as a result of the elliptical deformation of the
skyrmions by the application of the in-plane field.
