Dynamical phase diagram of the dc-driven underdamped Frenkel-Kontorova chain

The multistep dynamical phase transition from the locked to the running state of atoms in response to a dc external force is studied by molecular-dynamics simulations of the generalized Frenkel-Kontorova model in the underdamped limit. We show that the hierarchy of transition recently reported [Braun et al., Phys. Rev. Lett. 78, 1295 (1997)] strongly depends on the value of the friction constant. A simple phenomenological explanation for the friction dependence of the various critical forces separating intermediate regimes is given.