The Problem of critical damping in nanofriction

The progress that has been made in describing atomic friction in terms of mechanical instabilities of the stick-slip type masks the role of damping and makes researchers ignore the true mechanisms of dissipation. This study shows that there is a necessary condition for the realization of regular stick-slips occurring with atomic periodicity, which are observed in friction force microscopy (a variant of atomic force microscopy) experiments. This condition lies in the existence of a direct relation between the rate of dissipation and the characteristic frequency of a measuring system, i.e., its stiffness and mass ("critical damping"). The conclusion seems to be paradoxical; it indicates a nontrivial dissipation mechanism, which, according to the proposed explanation, essentially depends on memory effects.