Nonlinear flux diffusion in superimposed weak AC magnetic field

The influence of superimposed weak ac magnetic field on flux creep and relaxation phenomena is studied theoretically for a superconducting slab in superimposed dc and weak ac magnetic fields parallel to the slab surface. Nonlinear flux diffusion equations are solved with appropriate periodical boundary conditions, which describe the influence of the ac field component. The flux creep rate and magnetization decay are enhanced by the ac field as a result of rather strong nonlinearity of flux diffusion. The long-time relaxation profiles of electric field and shielding current change significantly as compared to the well-known stationary solutions in the absence of ac field. These results reflect rather general properties of nonlinear systems, namely the possibility of the large effect of small perturbations on the long-time behavior of a nonlinear system.