Friction Arising from Thermal Fields
The average velocity of a particle will decrease
if the particle interacts with a random force. This type of friction
originates from the theory of Brownian motion. In 1827, the British
botanist R. Brown was the first to report the irregular motion of
a pollen in a liquid. A theoretical description of Brownian motion
was provided by Einstein and Smoluchowski in the early twentienth
century. Later, it turned out that fluctuations and dissipation
are closely related. This relationship, known as fluctuation-dissipation
theorem, is encountered in many disciplines. Also, dissipation is
related to the phenomenon of decoherence encountered, for
example, in quantum mechanics.
In our investigations we study the friction experienced
by a particle due to its interaction with thermal electromagnetic
fields. These fields are generated by matter at finite temperatures.
The statistical correlation properties of thermal fields determine
the strength of the particle's dissipation. The statistical properties
depend on the geometry of the particle's environment as well as
the electromagnetic properties of particle and surrounding matter.
Our work is motivated by recent experiments that
measured friction acting on nanoscale probes near planar substrates
in ultra-high vacuum conditions. Existing theories lead to damping
coefficients that are orders of magnitude weaker than those measured
in experiments. Therefore, until recently, the physical picture
underlying friction in nanoscale systems was not clear. However,
our theory predicts that friction originates from electromagnetic
interactions between dielectric objects as opposed to metallic objects.
Furthermore, these interactions can penetrate through thin metal
layers which explains the previous discrepancy between theory and
experiment. More details on our theoretical approach can be found
in our preprint [PDF,