Composite multi-vortex diffraction-free beams and van Hove singularities in honeycomb lattices

TL;DR

This paper discovers diffraction-free multi-vortex beams in honeycomb optical lattices like graphene, analyzing their topological properties, effects of valley degrees of freedom, and changes at van Hove singularities, including formation of localized stripe patterns.

Contribution

It provides exact solutions for diffraction-free multi-vortex beams in honeycomb lattices and explores their topological and singularity-related properties, a novel insight in optical lattice physics.

Findings

Exact multi-vortex solutions in honeycomb lattices

Topological charge structures depend on valley and mass parameters

Stripe-shaped localized beams occur at van Hove singularities

Abstract

We find diffraction-free beams for graphene and MoS$_2$-type honeycomb optical lattices. The resulting composite solutions have the form of multi-vortices, with spinor topological charges ($n$, $n\pm1$). Exact solutions for the spinor components are obtained in the Dirac limit. The effects of the valley degree of freedom and the mass are analyzed. Passing through the van-Hove singularity the topological structure of the solutions is modified. Exactly at the singularity the diffraction-free beams take the form of strongly localized one-dimensional stripes.