Topological nodal-line semimetals in ferromagnetic rare-earth-metal monohalides

TL;DR

This paper predicts layered ferromagnetic rare-earth-metal monohalides as promising topological materials, including 2D Weyl semimetals, quantum anomalous Hall insulators, and 3D nodal-line semimetals, based on first-principles calculations.

Contribution

It identifies new layered ferromagnetic materials as hosts for various topological phases, expanding the class of materials for topological quantum phenomena.

Findings

Single-layer LaX and GdX are 2D Weyl semimetals and QAH insulators.

3D LaX and GdX exhibit robust nodal-line semimetals and weak QAHIs.

Nodal lines in 3D LaX are robust against spin-orbit coupling and near the Fermi level.

Abstract

Topological semimetals, extending the topological classification from insulators to metals, have greatly enriched our understanding of topological states in condensed matter. This is particularly true for topological nodal-line semimetals (TNLSs). In the present paper, we identify layered materials as promising candidates for hosting TNLSs. Based on first-principles calculations and effective model analysis, we propose that layered ferromagnetic rare-earth-metal monohalides LnX (Ln=La, Gd; X=Cl, Br) exhibit long pursued topological phases. Specifically, single-layer LaX and single-layer GdX are ideal two-dimensional (2D) Weyl semimetals and large-gap 2D quantum anomalous Hall insulators (QAHIs), with band gaps up to 61 meV, respectively. In addition, 3D LaX and 3D GdX are TNLSs with a pair of mirror-symmetry protected nodal lines and 3D weak QAHIs, respectively. The nodal lines in 3D LaX extending through the whole Brillouin zone (BZ) are fairly robust against strong spin-orbit coupling (SOC) and located close to the Fermi level, providing a novel platform toward exploring the exotic properties in nodal-line fermions as well as related device designs.