Dynamics of friction: superlubric state

Dynamics in friction is studied from an atomistic point of view. Friction is formulated as a problem of whether or not a given kinetic energy for the translational motion dissipates into the kinetic energies for the internal motions during sliding. From the study of the Frenkel-Kontorova model with kinetic energy terms, it is found that two different regimes appear in the parameter space specifying the model: the superlubricity and the friction regimes. The friction exactly vanishes in the superlubric regime and appears in the friction regime. The conditions for the superlubricity to occur are described. It is emphasized that a high dimensionality in the friction system is a key to understanding the physics of superlubricity. For high dimensional systems, superlubricity is a generic phenomenon, appearing for a wide class of (strong or weak) adhesion such as the metallic bonding and the van der Waals interaction. The results are discussed in comparison with those obtained by assuming the case where the upper surface slides quasi-statically against the lower surface.