Casimir effect between pinned particles in two-dimensional jammed systems

TL;DR

This paper demonstrates the existence of Casimir-like forces in two-dimensional jammed systems near the jamming transition, revealing a long-ranged repulsive force caused by particle clustering and pressure buildup.

Contribution

It introduces the observation of Casimir-like forces in classical jammed systems, expanding the understanding of fluctuation-induced forces beyond quantum and critical systems.

Findings

Long-ranged, repulsive Casimir-like force dominates near jamming transition.

Force arises from clustering of particles with strong contact forces.

Repulsive force increases as pinned particles approach each other.

Abstract

The Casimir effect arises when long-ranged fluctuations are geometrically confined between two surfaces, leading to a macroscopic force. Traditionally, these forces have been observed in quantum systems and near critical points in classical systems. Here we show the existence of Casimir-like forces between two pinned particles immersed in two-dimensional systems near the jamming transition. We observe two components to the total force: a short-ranged, depletion force and a long-ranged, repulsive Casimir-like force. The Casimir-like force dominates as the jamming transition is approached, and when the pinned particles are much larger than the ambient jammed particles. We show that this repulsive force arises due to a clustering of particles with strong contact forces around the perimeter of the pinned particles. As the separation between the pinned particles decreases, a region of high-pressure develops between them, leading to a net repulsive force.