Radiation from a dipole perpendicular to the interface between two planar semi-infinite magnetoelectric media

Abstract

We consider two semi-infinite magnetoelectric media with constant dielectric permittivity separated by a planar interface, whose electromagnetic response is described by non-dynamical axion electrodynamics and investigate the radiation of a point-like electric dipole located perpendicularly to the interface. We start from the exact Green's function for the electromagnetic potential, whose far-field approximation is obtained using a modified steepest descent approximation. This procedure yields the standard spherical waves as well as axially symmetric cylindrical superficial waves, which nevertheless are restricted to a region very close to the interface. We compute the angular distribution of the radiation and the total radiated power finding different interference patterns, depending on the relative position dipole-observer, and polarization mixing effects which are all absent in the standard dipole radiation. They are a manifestation of the magnetoelectric effect induced by axion electrodynamics. We illustrate our findings with some numerical estimations employing realistic media as well as some hypothetical choices in order to illuminate the effects of the magnetoelectric coupling which is usually very small.

Modification of transition radiation by three-dimensional topological insulators

“…(A1), (A2) and (A6) we obtain the four possible cases for a two layer configuration: observer and source at the upper medium, observer and source at the lower medium, observer at the upper medium and source at the lower one, and viceversa. In this appendix we apply the steepest descent method [68][69][70][71][72][73] to find the far-field approximation of the kintegrals of the reflective ( 17)-( 19) and transmissive electric fields ( 23)- (25). Nevertheless, we will only present the calculations for the x-component given by Eq.…”

“…Focusing on the radiation emitted by the particle, we will implement the far-field approximation. To this aim we employ a steepest descent method [68][69][70][71][72][73]. By means of this method, whose application with full details to the involved integrals is in Appendix B, we obtain the following results after dropping terms of order higher than r −2 for the electric field due to reflection…”

“…This result contrasts clearly with standard electrodynamics and reinforces the idea that the topological parameter mimics a permittivity as analyzed in Refs. [63,73] for other kind of radiations. After comparing the angular dependence of Eqs.…”