Electromagnetic radiation mediated by topological surface states

TL;DR

This paper investigates how topological surface states in insulators modify electromagnetic radiation from classical sources, deriving analytical corrections and analyzing specific emission scenarios.

Contribution

It provides the first analytical derivation of radiation modifications due to topological surface states within axion electrodynamics, including antenna emission and bremsstrahlung.

Findings

Surface Hall response causes azimuthal modulation in antenna radiation.

Radiation intensity from accelerated charges is uniformly reduced by a specific factor.

The results connect topological phases with observable electromagnetic phenomena.

Abstract

We study electromagnetic radiation from classical sources near a planar interface separating a topological and a trivial insulator, modeled within axion electrodynamics. The system features a piecewise constant $\theta$-term that encodes the magnetoelectric response of topological surface states. Treating this coupling perturbatively, we derive analytical corrections to the standard Li\'enard-Wiechert potentials and obtain modified radiation fields in the far zone. As applications, we analyze the emission from linear antennas and the bremsstrahlung radiation of accelerated charges near the interface. For antennas, the surface Hall response breaks axial symmetry and produces azimuthal modulations that grow with the electrical length, leading to distinct scaling behaviors in the total and angular radiated power. {For accelerated charges, the emitted intensity is uniformly reduced by a factor $1 - (\sigma_{\mathrm{Hall}} / 2\epsilon v)^2$, which we interpret as a process-specific attenuation of the radiative strength due to interference with its image magnetic monopole inside the topological medium.} These results reveal how topological surface states mediate measurable modifications to classical radiation, establishing a link between axion electrodynamics, topological phases, and field theories with spatially varying couplings.