Theoretical realization of two-dimensional half-metallicity and fully spin-polarized multiple nodal-line fermions in monolayer PrOBr

Two-dimensional (2D) half metallicity and topological aspects of matter are the focus of current research because of the promising applications in nanoscale spintronics and quantum electronics. In this work, we report the perfect combination of half-metallic properties and electronic topological properties in single 2D phase, namely, the PrOBr monolayer. The material only possesses conducting electrons in the spin-up channel, while it shows a large insulating gap of 3.5 eV in the spin-down channel with the Curie temperature as high as 423 K. In the conducting spin channel, it exhibits multiple band crossings, which can surprisingly realize the coexistence of fully spin-polarized open/closed, and type-I/type-II/hybrid-type nodal lines. The coexistence of so many nodal line states has been neither identified in 2D materials nor identified in half metals before. The protection mechanism, the spin-orbit coupling impact, and the effective models for the nodal lines have been clarified. Our results suggest that the PrOBr monolayer is a good electronic material with (i) 2D half metallicity; (ii) multiple nodal lines of 100% spin polarization.