Two-dimensional nodal-loop half-metal in monolayer MnN
Authors: Wang, SS; Yu, ZM; Liu, Y; Jiao, YL; Guan, S; Sheng, XL; Yang, SYA
PHYSICAL REVIEW MATERIALS
Volume: 3 Issue: 8 Published: AUG 7 2019 Language: English Document type: Article
Two-dimensional (2D) materials with nodal-loop band crossing have been attracting great research interest. However, it remains a challenge to find 2D nodal loops that are robust against spin-orbit coupling (SOC) and realized in magnetic states. Here, based on first-principles calculations and theoretical analysis, we predict that monolayer MnN is a 2D nodal-loop half-metal with fully spin-polarized nodal loops. We show that monolayer MnN has a ferromagnetic ground state with out-of-plane magnetization. Its band structure shows half metallicity with three low-energy bands belonging to the same spin channel. The crossing between these bands forms two concentric nodal loops centered around the Gamma point near the Fermi level. Remarkably, the nodal loops and their spin polarization are robust under SOC due to the protection of a mirror symmetry. We construct an effective model to characterize the fully polarized emergent nodal-loop fermions. We also find that a uniaxial strain can induce a loop transformation from a localized single loop circling around Gamma to a pair of extended loops penetrating the Brillouin zone.