Flux front penetration in disordered superconductors

We investigate flux front penetration in a disordered type-II superconducto r by molecular dynamics simulations of interacting vortices and find scalin g laws for the front position and the density profile. The scaling can be u nderstood by performing a coarse graining of the system and writing a disor dered nonlinear diffusion equation. Integrating numerically the equation, w e observe a crossover from hat to fractal front penetration as the system p arameters are varied. The value of the fractal dimension indicates that the invasion process is described by gradient percolation.