Cu-substituted lead phosphate apatite as an inversion-asymmetric Weyl semimetal

TL;DR

This paper predicts that copper-substituted lead phosphate apatite (`LK-99') is an inversion-asymmetric Weyl semimetal with unique Weyl nodes and Fermi arc states, based on symmetry and density functional theory analyses.

Contribution

It demonstrates, using symmetry arguments and density functional calculations, that `LK-99' hosts unconventional Weyl nodes with charges of ±2 and associated topological surface states.

Findings

Identifies Weyl nodes with charges of ±2 near Γ and A points.

Shows existence of topologically protected Fermi arc surface states.

Analyzes effects of spin-orbit coupling on the band structure.

Abstract

Based on symmetry arguments and the latest density functional results for the copper-substituted lead phosphate apatite (`LK-99'), we show that, at the non-interacting level, the material is an inversion-asymmetric Weyl semimetal. A pair of Weyl nodes with opposite chiralities emerge at different energies in the vicinity of the time-reversal-invariant $\Gamma$ and ${\rm A}$ points of the 3D Brillouin zone. These are characterized by unusual Weyl charges of $C_{\rm W} = \pm 2$ and are connected by two branches of topologically protected Fermi arc states on surfaces parallel to the principal $c$-axis. We further study important effects of the atomic spin-orbit coupling on the band structure and the electronic properties of the material in general. Possible implications of the proposed band topology on the strong correlation physics are also discussed.