Creep motion of an elastic string in a random potential

We study the creep motion of an elastic string in a two dimensional pinning landscape by Langevin dynamics simulations. We find that the Velocity-Force characteristics are well described by the creep formula predicted from phenomenological scaling arguments. We analyze the creep exponent $\mu$, and the roughness exponent $\zeta$. Two regimes are identified: when the temperature is larger than the strength of the disorder we find $\mu \approx 1/4$ and $\zeta \approx 2/3$, in agreement with the quasi-equilibrium-nucleation picture of creep motion; on the contrary, lowering enough the temperature, the values of $\mu$ and $\zeta$ increase showing a strong violation of the latter picture.