Uphill Drift in the Absence of Current in Single-File Diffusion

Area of Science:

• Physics
• Physical Chemistry
• Statistical Mechanics

Background:

• Single-file diffusion models transport in confined systems like porous media.
• Particles in such systems cannot overtake each other, leading to unique dynamics.
• An external potential gradient is applied across a 1D channel system.

Purpose of the Study:

• To investigate the anomalous transport of a tracer particle in a single-file system with an asymmetric external potential.
• To analyze the emergent drift behavior of a tracer particle against the potential gradient.

Main Methods:

• Analytical calculation of the first two moments of the tracer particle's position.
• Extensive numerical simulations to validate analytical findings.
• Modeling of Brownian colloidal particles in a one-dimensional channel.

Main Results:

• A single-file tracer particle exhibits an average uphill drift towards the region of higher potential.
• This anomalous drift follows a late-time power-law behavior: ⟨Y(t)⟩ ∝ t^{1/4}.
• The drift contradicts equilibrium predictions where no net current is expected.

Conclusions:

• The study reveals a surprising emergent drift phenomenon in single-file diffusion systems.
• The findings highlight the complex dynamics arising from confinement and external potentials.
• The results have implications for understanding transport in complex porous media and nanoscale channels.