Simulations of the onset of diffusion in a flux-line lattice in a random potential

We simulate the finite-temperature dynamics of flux lines in a thin film. It is shown that a weak random potential significantly reduces the temperature, TD, at which flux lines start to diffuse and dissipation sets in. The diffusion starts to take place along grain boundaries in the flux-line lattice. These findings are discussed in relation to the magnetic properties of the high-temperature superconductors.