Anharmonic particles: suppressing van der Waals forces by an external field

TL;DR

This paper investigates how strong external electric fields can suppress van der Waals forces between particles with anharmonic dipole interactions, providing analytical insights and potential control mechanisms.

Contribution

It introduces a model of anharmonic particles with saturating dipole moments and analyzes how external fields influence Casimir forces, including a simple asymptotic formula.

Findings

External electric fields can significantly reduce Casimir forces.

Force suppression depends on the angle between the field and particle axis.

A simple formula describes force behavior at large external fields.

Abstract

We study the classical thermal component of Casimir, or van der Waals, forces between point particles with highly anharmonic dipole Hamiltonians when they are subjected to an external electric field. Using a model for which the individual dipole moments saturate in a strong field (a model that mimics the charges in a neutral, perfectly conducting sphere), we find that the resulting Casimir force depends strongly on the strength of the field, as demonstrated by analytical results. For a certain angle between external field and center to center axis, the fluctuation force can be tuned and suppressed to arbitrarily small values. We compare the forces between these anharmonic particles to those between harmonic ones, and also provide a simple formula for asymptotically large external fields, which we expect to be generally valid for the case of saturating dipole moments.