Non-contact Friction and Relaxational Dynamics of Surface Defects

Details Non-contact Friction and Relaxational Dynamics of Surface Defects Non-contact Friction and Relaxational Dynamics of Surface Defects

2012-01-30

arxiv.org/abs/1201.6378v1

Phys. Rev. Lett. 108, 136101 (2012)

Physics

Condensed Matter

Mesoscale and Nanoscale Physics

5 pages, 4 figures, accepted for publication in Physical Review Letters

Scientific paper

10.1103/PhysRevLett.108.136101

Motion of cantilever near sample surfaces exhibits additional friction even before two bodies come into mechanical contact. Called non-contact friction (NCF), this friction is of great practical importance to the ultrasensitive force detection measurements. Observed large NCF of a micron-scale cantilever found anomalously large damping that exceeds theoretical predictions by 8-11 orders of magnitude. This finding points to contribution beyond fluctuating electromagnetic fields within van der Waals approach. Recent experiments reported by Saitoh et al. (Phys. Rev. Lett. 105, 236103 (2010)) also found nontrivial distance dependence of NCF. Motivated by these observations, we propose a mechanism based on the coupling of cantilever to the relaxation dynamics of surface defects. We assume that the surface defects couple to the cantilever tip via spin-spin coupling and their spin relaxation dynamics gives rise to the backaction terms and modifies both the friction coefficient and the spring constant. We explain the magnitude, as well as the distance dependence of the friction due to these backaction terms. Reasonable agreement is found with the experiments.

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