Fully spin-polarized nodal chain state in half metal LiV$_2$O$_4$

TL;DR

This paper predicts a fully spin-polarized nodal chain state in the half-metallic ferromagnet LiV$_2$O$_4$, revealing a new topological state with potential spintronics applications through first-principles calculations.

Contribution

It introduces the first realistic material, LiV$_2$O$_4$, exhibiting a fully spin-polarized nodal chain state protected by symmetries, expanding the landscape of topological materials.

Findings

Identification of spin-polarized nodal loops in LiV$_2$O$_4$

Formation of chain-like nodal structure from nodal loops

Presence of fully spin-polarized surface states

Abstract

Nodal-chain fermions, as novel topological states of matter, have been hotly discussed in non-magnetic materials. Here, by using first-principles calculations and symmetry analysis, we propose the realization of fully spin-polarized nodal chain in the half-metal state of LiV$_2$O$_4$ compound. The material naturally shows a ferromagnetic ground state, and takes on a half-metal band structure with only the bands from the spin-up channel present near the Fermi level. The spin-up bands cross with each other, which form two types of nodal loops. These nodal loops arise from band inversion and are under the protection of the glide mirror symmetries. Remarkably, we find the nodal loops conjunct with each other and form chain-like nodal structure. Correspondingly, the w-shaped surface states are also fully spin-polarized. The fully spin-polarized nodal chain identified here has not been proposed in realistic materials before. An effective model is constructed to describe the nature of nodal chain. The effects of the electron correlation, the lattice strains, and the spin-orbit coupling are discussed. The fully spin-polarized bulk nodal-chain and the associated nontrivial surface states for a half-metal may open novel applications in spintronics.