From triple-point materials to multiband nodal links

We study a class of topological materials which in their momentum-space band structure exhibit three-fold degeneracies known as triple points. Focusing specifically on $\mathcal{P}\mathcal{T}$-symmetric crystalline solids with negligible spin-orbit coupling, we find that such points can be stabilized by little groups containing three-, four- or six-fold rotation axis, and develop classification all possible type A vs. B according to the absence presence attached nodal-line arcs. Furthermore, employing recently discovered non-Abelian topology, argue rotation-symmetry-breaking strain transforms type-A into multiband nodal links. Although compositions were previously theoretically conceived related monopole charges, practical condensed-matter platform for manipulation inspection has hitherto been missing. By reviewing triple-point weak performing first-principles calculations predict new ones, identify suitable candidates realization links applied strain. In particular, report an ideal compound this phenomenon is Li$_2$NaN, conversion facilitates largely tunable density states optical conductivity doping strain, respectively.