Nanoscale Friction: Kinetic Friction of Magnetic Flux Quanta and Charge Density Waves

In analogy with the standard macroscopic friction, here we present a comparative study of the friction force felt by moving vortices in superconductors and charge density waves. Using experiments and a model for this data, our observations (1) provide a link between friction at the micro- and macroscopic scales, (2) explain the roundness of the static-kinetic friction transition in terms of thermal fluctuations, particle interactions, and system size (critical-phenomena view), and (3) explain the crossing of the kinetic friction F_k versus velocity V for our pristine (high density of very weak defects) and our irradiated samples (with lower density of deeper pinning defects).