Single pair of type-III Weyl points half-metals: BaNiIO6 as an example

The realization of Weyl systems with the minimum nonzero number of Weyl points (WPs) and full spin polarization remains challenging in topology physics and spintronic. In this paper, we used first-principles calculations and symmetry analysis to demonstrate that ${\mathrm{BaNiIO}}_{6}$, a dynamically and thermodynamically stable half-metallic material, hosts fully spin-polarized single-pair (SP) WPs with a charge number ($\mathcal{C}$) of $\ifmmode\pm\else\textpm\fi{}2$ and a type-III band dispersion around the Fermi level. Moreover, the fully spin-polarized SP-WPs induce double-helicoid Fermi arcs on the ($10\overline{1}0$) surface. The half-metallic state and the spin-polarized SP-WPs are robust to uniform strains (from $\ensuremath{-}10$ to $+8%$) and onsite Hubbard-Coulomb interactions (from 0 to 6 eV). When $+9$ or $+10%$ uniform strain is applied to the ${\mathrm{BaNiIO}}_{6}$ system, it hosts six additional type-II WPs with $|\mathcal{C}|=1$ in the three-dimensional Brillouin zone in addition to the two type-III WPs with $|\mathcal{C}|=2$. We hope that this paper will motivate future research into SP-WPs half-metals.