Thermal contact delocalization in atomic scale friction: a multitude of friction regimes

This paper summarizes and extends results from a series of recent investigations of atomic scale friction, in which an ultra-low effective mass and a corresponding thermal delocalization of the contact play a dominant role. A rich variety of physically different regimes of friction concerned with the contact delocalization are analyzed in a systematic way and visualized by advanced numerical calculations. The results shed an essentially new light on what is actually measured in friction force microscopy and suggest the necessity to reinterpret many seemingly standard experiments. Even more importantly, our results can possibly be extended to the asperities that establish the contact between two sliding bodies thus predicting a much more pronounced role of thermally driven dynamics in macroscopic sliding than has ever been imagined. The paper is supplied with a detailed introduction to the subject, aimed at a general physical audience.