Journal Article

Self-diffusion anomalies of an odd tracer in soft-core media

Luigi Muzzeddu, Pietro, Metzler, Ralf, Kalz, Erik, Sharma, Abhinav, Gambassi, Andrea

2025

Overview

Odd-diffusive systems, characterised by broken time-reversal and/or parity, have recently been shown to display counterintuitive features such as interaction-enhanced dynamics in the dilute limit. Here we extend the investigation to the high-density limit of an odd tracer embedded in a soft medium described by the Gaussian core model (GCM) using a field-theoretic approach based on the Dean–Kawasaki equation. Our analysis reveals that interactions can enhance the dynamics of an odd tracer even in dense systems. We demonstrate that oddness results in a complete reversal of the well-known self-diffusion ( D s ) anomaly of the GCM. Ordinarily, D s exhibits a non-monotonic trend with increasing density, approaching but remaining below the interaction-free diffusion, D 0 , ( D s < D 0 ) so that D s ↑ D 0 at high densities. In contrast, for an odd tracer, self-diffusion is enhanced ( D s > D 0 ) and the GCM anomaly is inverted, displaying D s ↓ D 0 at high densities. The transition between the standard and reversed GCM anomaly is governed by the tracer’s oddness, with a critical oddness value at which the tracer diffuses as a free particle ( D s ≈ D 0 ) across all densities. We validate our theoretical predictions with Brownian dynamics simulations, finding strong agreement between the them.

• Publisher: IOP Publishing
• Subject: Approximation / Dean–Kawasaki equation / Density / Equilibrium / Gaussian core model / interacting colloids / Investigations / odd diffusion / Physics / Polymers / Self diffusion / self-diffusion anomaly / Simulation / stochastic field theory / weak-coupling approximation