Demonstration of the existence of biased transportation in the asymmetric nanoscale systems induced by thermal noise from a simple mathematics perspective

TL;DR

This paper demonstrates mathematically that biased directional transport can occur in asymmetric nanoscale systems at room temperature due to non-white thermal noise, supporting MD simulation observations.

Contribution

It provides a simple mathematical explanation for biased transport in nanoscale systems, highlighting the role of colored thermal noise.

Findings

Biased transport exists in MD simulations of nanoscale systems.

Thermal noise at nanoscale is colored, not white, with a correlation time of about 10 ps.

Non-white noise explains the net flux observed in asymmetric nanochannels.

Abstract

The existence of net flux across the nanochannels under the asymmetrical static electric fields obtained at room temperature from molecular dynamics (MD) simulations [Nat. Nanotechnol. 2, 709 (2007); Phys. Rev. Lett. 101, 064502 (2008)] has been extensively queried on whether the second law of the thermodynamics holds, and whether the observations result from the numerical artifacts. Here we use a simple mathematics to demonstrate the existence of biased-directional transportation (net flux across the channel) in those asymmetrical nanoscale systems at room temperature, at least in the MD simulations. We find that the key to the existence of biased-directional transportation is that the thermal noise is not white anymore at nanoscale; it includes the color noise with an autocorrelation time length (for MD simulation, this length is of ~10 ps).