We report measurements of noncontact friction between surfaces of NbSe2 and SrTiO3, and a sharp Pt-Ir tip that is oscillated laterally by a quartz tuning fork cantilever. At 4.2 K, the friction coefficients on both the metallic and insulating materials show a giant maximum at the tip-surface distance of several nanometers. The maximum is strongly correlated with an increase in the spring constant of the cantilever. These features can be understood phenomenologically by a distance-dependent relaxation mechanism with distributed time scales.
@article{arxiv.1012.2434,
title = {Gigantic Maximum of Nanoscale Noncontact Friction},
author = {Kohta Saitoh and Kenichi Hayashi and Yoshiyuki Shibayama and Keiya Shirahama},
journal= {arXiv preprint arXiv:1012.2434},
year = {2010}
}