Jian-Huang She, Alexander V. Balatsky
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.
View original:
http://arxiv.org/abs/1201.6378
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