Fully spin-polarized nodal loop semimetals in alkaline-metal monochalcogenide monolayers

Abstract

Topological semimetals in ferromagnetic materials have attracted enormous attention due to the potential applications in spintronics. Using the first-principles density functional theory together with an effective lattice model, here we present a new family of topological semimetals with a fully spin-polarized nodal loop in alkaline-metal monochalcogenide $MX$ ($M$ = Li, Na, K, Rb, Cs; $X$ = S, Se, Te) monolayers. The half-metallic ferromagnetism can be established in $MX$ monolayers, in which one nodal loop formed by two crossing bands with the same spin components is found at the Fermi energy. This nodal loop half-metal survives even when considering the spin-orbit coupling owing to the symmetry protection provided by the ${\mathcal{M}}_z$ mirror plane. The quantum anomalous Hall state and Weyl-like semimetal in this system can be also achieved by rotating the spin from the out-of-plane to the in-plane direction. The $MX$ monolayers hosting rich topological phases thus offer an excellent materials platform for realizing the advanced spintronics concepts.

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• Two-dimensional half Chern-Weyl semimetal with multiple screw axes
• Intrinsic and extrinsic anomalous transport properties of Heusler ferromagnets Fe${}_2$CoAl and Fe${}_2$NiAl from first principles
• Intrinsic and extrinsic anomalous transport properties in noncollinear antiferromagnetic Mn${}_3$Sn from first-principle calculations