Electromagnetic properties of viscous charged fluids

TL;DR

This paper develops a theoretical framework to describe how viscosity in charged fluids affects electromagnetic wave behavior, revealing multiple evanescent modes, negative refraction, and altered reflectivity, with implications for optical probing of such materials.

Contribution

It introduces a comprehensive model linking viscosity to electromagnetic properties, including analytical expressions for reflection and transmission, and predicts novel phenomena like negative refraction and oscillatory field intensities.

Findings

Finite viscosity causes multiple evanescent wave modes.

Viscosity reduces reflectivity and increases field penetration.

Oscillations of electromagnetic field intensity occur inside the material.

Abstract

We provide a general theoretical framework to describe the electromagnetic properties of viscous charged fluids, consisting for example of electrons in certain solids or plasmas. We confirm that finite viscosity leads to multiple modes of evanescent electromagnetic waves at a given frequency, one of which is characterized by a negative index of refraction, as previously discussed in a simplified model by one of the authors. In particular we explain how optical spectroscopy can be used to probe the viscosity. We concentrate on the impact of this on the coefficients of refraction and reflection at the sample-vacuum interface. Analytical expressions are obtained relating the viscosity parameter to the reflection and transmission coefficients of light. We demonstrate that finite viscosity has the effect to decrease the reflectivity of a metallic surface, while the electromagnetic field penetrates more deeply. While on a phenomenological level there are similarities to the anomalous skin effect, the model presented here requires no particular assumptions regarding the corpuscular nature of the charge liquid. A striking consequence of the branching phenomenon into two degenerate modes is the occurrence in a half-infinite sample of oscillations of the electromagnetic field intensity as a function of distance from the interface.