Axions, Surface States, and the Post Constraint in Electromagnetics

TL;DR

This paper demonstrates that the axionic component in electromagnetic materials does not influence Maxwell's equations or boundary conditions, and observed effects are due to surface states, confirming the Post constraint.

Contribution

It provides a theoretical validation of the Post constraint by showing the axionic piece vanishes and identifies surface states as the source of observable effects.

Findings

Axionic piece vanishes from Maxwell equations and boundary conditions.

Surface states, not axionic effects, explain experimental observations.

The Post constraint is theoretically supported.

Abstract

After formulating the frequency-domain Maxwell equations for a homogeneous, linear, bianisotropic material occupying a bounded region, we found that the axionic piece vanishes from both the differential equations valid in the region and the boundary conditions, thereby vindicating the Post constraint. Our analysis indicates that characteristic effects that may be observed experimentally with magnetoelectric materials are not the consequences of the axionic piece but of an admittance that describes surface states.