Crystalline topological Dirac semimetal phase in rutile structure β'-PtO₂

Based on first-principles calculations and symmetry analysis, we propose that a transition metal rutile oxide, in particular $\beta'$-PtO$_2$, can host a three-dimensional topological Dirac semimetal phase. We find that $\beta'$-PtO$_2$ possesses a linked nodal rings structure when spin-orbit coupling is neglected. Incorporating spin-orbit coupling gaps the nodal rings, while preserving a single pair of three-dimensional Dirac points protected by a screw rotation symmetry. This Dirac point is created by a band inversion of two $d$ bands, which is a realization of a DSM phase in correlated electron systems. Moreover, a mirror plane in the momentum space carries a nontrivial mirror Chern number $n_M = -2$, which distinguishes $\beta'$-PtO$_2$ from the Dirac semimetals known so far, such as Na$_3$Bi and Cd$_3$As$_2$. If we apply a perturbation that breaks the rotation symmetry and preserves the mirror symmetry, the Dirac points are gapped and the system becomes a topological crystalline insulator.