Electronic and phononic friction of solids at low temperatures

It has recently been shown both experimentally and theoretically that there is no static friction in a contact of atomically flat crystalline solids p rovided the periods of their lattices are incommensurate and their interact ion does not exceed some critical value. The only mechanisms of friction in this case are phonon generation and excitation of conducting electrons. It is shown that, at low temperatures, the phonon contribution to the coeffic ient of friction can be very small by virtue of the quantum mechanical natu re of the elementary excitations in a solid. Incommensurate dielectric crys tals could therefore slip at low temperatures practically without friction. In metals, on the contrary. the excitation of electrons leads to a finite dynamic friction force at any temperature. Presently, both phonon and elect ron contributions to the friction force are estimated (the latter both in t he normal and the superconducting state of metal). (C) 2001 Elsevier Scienc e Ltd. All rights reserved.