Extinction of coherent backscattering by a disordered photonic crystal with a Dirac spectrum

TL;DR

This paper demonstrates that in a disordered photonic crystal with a Dirac spectrum, the Berry phase causes the extinction of coherent backscattering, confirmed through numerical and analytical methods.

Contribution

It reveals how the Berry phase suppresses coherent backscattering in a disordered photonic crystal near the Dirac point, combining numerical simulations with analytical Dirac equation predictions.

Findings

Berry phase causes extinction of coherent backscattering

Numerical solutions confirm analytical predictions

Destructive interference suppresses reflected intensity

Abstract

Photonic crystals with a two-dimensional triangular lattice have a conical singularity in the spectrum. Close to this so-called Dirac point, Maxwell's equations reduce to the Dirac equation for an ultrarelativistic spin-1/2 particle. Here we show that the half-integer spin and the associated Berry phase remain observable in the presence of disorder in the crystal. While constructive interference of a scalar (spin-zero) wave produces a coherent backscattering peak, consisting of a doubling of the disorder-averaged reflected photon flux, the destructive interference caused by the Berry phase suppresses the reflected intensity at an angle which is related to the angle of incidence by time-reversal symmetry. We demonstrate this extinction of coherent backscattering by a numerical solution of Maxwell's equations and compare with analytical predictions from the Dirac equation.