Oscillatory force autocorrelations in equilibrium odd-diffusive systems

TL;DR

This paper reveals that in equilibrium odd-diffusive systems, the force autocorrelation function can oscillate and become negative, leading to enhanced particle diffusion, which challenges traditional assumptions about monotonic decay in such functions.

Contribution

The study analytically demonstrates oscillatory and negative FACF in odd-diffusive systems and highlights the importance of the full autocorrelation tensor for understanding dynamics.

Findings

FACF can become negative and oscillate in odd-diffusive systems

Full autocorrelation tensor, including antisymmetric parts, is necessary for dynamics description

Particle interactions can enhance self-diffusion in these systems

Abstract

The force autocorrelation function (FACF), a concept of fundamental interest in statistical mechanics, encodes the effect of interactions on the dynamics of a tagged particle. In equilibrium, the FACF is believed to decay monotonically in time which is a signature of slowing down of the dynamics of the tagged particle due to interactions. Here we analytically show that in odd-diffusive systems, which are characterized by a diffusion tensor with antisymmetric elements, the FACF can become negative and even exhibit temporal oscillations. We also demonstrate that, despite the isotropy, the knowledge of FACF alone is not sufficient to describe the dynamics: the full autocorrelation tensor is required and contains an antisymmetric part. These unusual properties translate into enhanced dynamics of the tagged particle quantified via the self-diffusion coefficient that, remarkably, increases due to particle interactions.