Pseudospin-2 in photonic chiral borophene

Pseudospin is an angular momentum degree of freedom introduced in analogy to the real electron spin in the effective massless Dirac-like equation used to describe wave evolution at conical intersections such as the Dirac cones of graphene. Here, we study a photonic implementation of a chiral borophene allotrope hosting a pseudospin-2 conical intersection in its energy-momentum spectrum. The presence of this fivefold spectral degeneracy gives rise to quasiparticles with pseudospin up to $\pm2$. We report on conical diffraction and pseudospin-orbit interaction of light in photonic chiral borophene, which, as a result of topological charge conversion, leads to the generation of highly charged optical phase vortices.