Sample dependence of the Casimir force

TL;DR

This paper investigates how sample-dependent variations in gold films' optical properties affect the Casimir force, emphasizing the importance of precise dielectric function data for accurate force predictions.

Contribution

It demonstrates that film deposition conditions significantly alter dielectric functions, impacting Casimir force calculations and establishing upper limits based on perfect crystalline gold.

Findings

Dielectric functions vary with deposition conditions.

Force between films is smaller than between bulk samples.

Minimal force reduction is about 2% at small separations.

Abstract

Difference between bulk material and deposited film is shown to have an appreciable influence on the Casimir force. Analysis of the optical data on gold films unambiguously demonstrates the sample dependence: the dielectric functions of the films deposited in different conditions are different on the level that cannot be ignored in high precision prediction of the force. It is argued that the precise values of the Drude parameters are crucial for accurate evaluation of the force. The dielectric function of perfect single crystalline gold is discussed. It is used to establish the upper limit on the absolute value of the force. It is demonstrated that the force between films is smaller than that between bulk samples mainly due to the presence of voids and electron scattering on the grain boundaries in the films. The minimal reduction of the force is estimated as 2% for the smallest separations investigated in the most precise experiments. The other sample effects can reduce the force further but the correction is expected to be smaller than 1%.