Retardation turns the van der Waals attraction into Casimir repulsion already at 3 nm

TL;DR

This paper demonstrates that retardation effects can induce Casimir repulsion at very small separations (~3 nm), challenging the conventional understanding that such effects only occur at larger distances.

Contribution

It reveals that retardation effects cause Casimir repulsion at nanometer scales, a phenomenon not previously observed at such small distances.

Findings

Retardation effects induce Casimir repulsion at around 3 nm.

Van der Waals forces remain attractive at all separations.

Retardation effects are typically associated with larger distances.

Abstract

Casimir forces between surfaces immersed in bromobenzene have recently been measured by Munday et al. Attractive Casimir forces were found between gold surfaces. The forces were repulsive between gold and silica surfaces. We show the repulsion is due to retardation effects. The van der Waals interaction is attractive at all separations. The retardation driven repulsion sets in already at around 3 nm. To our knowledge retardation effects have never been found at such a small distance before. Retardation effects are usually associated with large distances.