Magnetic wallpaper Dirac fermions and topological magnetic Dirac insulators

TL;DR

This paper introduces topological magnetic Dirac insulators (TMDIs) with surface Dirac fermions protected by magnetic wallpaper symmetries, proposing candidate materials and a search scheme to advance magnetic topological crystalline insulator research.

Contribution

The paper proposes a new class of magnetic topological insulators with fourfold-degenerate Dirac fermions protected by magnetic wallpaper groups, and suggests candidate materials based on first-principles calculations.

Findings

Identification of TMDIs with protected surface Dirac fermions

Proposal of candidate materials Nd4Te8Cl4O20 and DyB4

Development of a scheme to search for TMDIs using space group analysis

Abstract

Topological crystalline insulators (TCIs) can host anomalous surface states which inherits the characteristics of crystalline symmetry that protects the bulk topology. Especially, the diversity of magnetic crystalline symmetries indicates the potential for novel magnetic TCIs with distinct surface characteristics. Here, we propose a topological magnetic Dirac insulator (TMDI), whose two-dimensional surface hosts fourfold-degenerate Dirac fermions protected by either the $p'_c4mm$ or $p4'g'm$ magnetic wallpaper group. The bulk topology of TMDIs is protected by diagonal mirror symmetries, which give chiral dispersion of surface Dirac fermions and mirror-protected hinge modes. We propose candidate materials for TMDIs including Nd$_4$Te$_8$Cl$_4$O$_{20}$ and DyB$_4$ based on first-principles calculations, and construct a general scheme for searching TMDIs using the space group of paramagnetic parent states. Our theoretical discovery of TMDIs will facilitate future research on magnetic TCIs and illustrate a distinct way to achieve anomalous surface states in magnetic crystals.