Monoclinic SrIrO-a Dirac semimetal produced by non-symmorphic symmetry and spin-orbit coupling.

SrIrO crystallizes in a monoclinic structure of distorted hexagonal perovskite at ambient pressure. The transport measurements show that the monoclinic SrIrO is a low-carrier density semimetal, as in the orthorhombic perovskite polymorph. The electronic structure calculation indicates a semimetallic band structure with Dirac bands at two high-symmetry points of Brillouin zone only when spin-orbit coupling is incorporated, suggesting that the semimetallic state is produced by the strong spin-orbit coupling. We argue that the Dirac bands are protected by the non-symmorphic symmetry of lattice.