Transverse thermal depinning and nonlinear sliding friction of an adsorbedmonolayer

We study the response of an adsorbed monolayer under a driving force as a m odel of sliding friction phenomena between two crystalline surfaces with a boundary lubrication layer Using Langevin-dynamics simulation, we determine the nonlinear response in the direction transverse to a high symmetry dire ction along which the layer is already sliding. We find that below a finite transition temperature there exist a critical depinning force and hysteres is effects in the transverse response in the dynamical state when the adlay er is sliding smoothly along the longitudinal direction.