Topological Dirac semimetallic phase in transition metal compounds

It is known that the transition metal monoarsenides/phosphides (TaAs, TaP, NbAs, and NbP) are Weyl semimetals that can host the long-sought Majorana fermions. Motivated by these exciting findings, we find that some of their allotropes reveal three-dimensional Dirac points. Based on the classification of three-dimensional topological Dirac semimetals proposed by Yang and Nagaosa (Nat. Commun. \textbf{5}, 4898 (2014)), the nontrivial topology is confirmed by computing the corresponding topological invariant. That is, we propose a new family of topological Dirac semimetals other than $\mathrm{Na_3Bi}$ and $\mathrm{Cd_3As_2}$. Besides, our results also indicate that the crystal symmetry plays an important role in determining the properties of the Dirac states and topological phase.