Thermolubricity and the Jarzynski equality

Two different pieces of physics in nanoscale sliding friction are thermolubricity and the Jarzynski identity. The first: a dry slider can at high temperature and low velocity exhibit thermolubric friction f ∝ v replacing ordinary stick–slip friction f ∝ logv in opposite conditions. The second: satisfaction (violation) of Jarzynski’s identity is tied to the abundance (scarcity) of negative work events (“free lunches”). Thermolubricity and Jarzynski are general in nature and separately met in experiments including sliding emulations in optical lattices, and protein force spectroscopy. We prove analytically and demonstrate numerically in the classical Prandtl-Tomlinson point slider model that the presence or absence of thermolubricity is exactly equivalent to satisfaction or violation of the Jarzynski equality. The divide between the two regimes simply coincides with the total frictional work per cycle falling below or above kT respectively. This concept can, with due caution, be extended to more complex sliders, and invites crosscheck experiments, such as searching for free lunches in cold ion sliding as well as in forced protein unwinding, and alternatively checking for a thermolubric regime in dragged colloid monolayers.