Probing the response of metals to low-frequency s-polarized evanescent fields

TL;DR

This paper proposes an experimental method to test how metals respond to low-frequency s-polarized evanescent fields by measuring magnetic fields, aiming to resolve discrepancies in theoretical models like Drude and plasma responses.

Contribution

It introduces a novel experimental approach to distinguish between Drude and plasma models for metal response using magnetic field measurements of evanescent waves.

Findings

Magnetic field responses differ significantly between models.

Measurement can discriminate between Drude and plasma responses.

Results have implications for Casimir force theory.

Abstract

Experimental test for the response function of metals to the low-frequency s-polarized evanescent waves is proposed by measuring the lateral component of magnetic field of an oscillating magnetic dipole spaced above a thick metallic plate. This suggestion is motivated by the fact that the Lifshitz theory using the Drude response function is in contradiction with high-precision measurements of the Casimir force performed at separations exceeding 150~nm. Analytic expressions for the lateral components of the magnetic field, which are fully determined by the s-polarized evanescent waves, are reported in terms of the reflection coefficients of the plate metal. Numerical computations are performed for the reasonable values of the experimental parameters for different models of the dielectric response. The resulting fields differ by the orders of magnitude depending on whether the Drude or plasma response function is used in computations. Thus, the measurement of the magnetic field will allow to discriminate between these two options. Possible applications of the obtained results are discussed.