Topological crystalline semimetals in non-symmorphic lattices without time-reversal symmetry

Numerous efforts have been devoted to reveal exotic semimetallic phases with topologically non-trivial bulk and surface states in materials with strong spin-orbit coupling. Recent theoretical works on orthorhombic perovskite iridates SrIrO3 have indicated that non-symmorphic symmetry is crucial to protect a nodal line Fermi surface (FS) in addition to space-time inversion symmetry [C. Fang {\it et.al}, PRB {\bf 92}, 081201(R) (2015), Y. Chen {\it et.al}, Nat. Commu. {\bf 6}, (2015)]. In this work, we investigate possible topological semimetals in the absence of time-reversal symmetry. In principle, an anti-unitary operator, defined as a product of time-reversal and glide operators, can protect a four-fold or two-fold degenerate nodal FS. Indeed this happens in SrIrO3 with the magnetic field along a particular direction. A trivial gapped insulator can also occur due to a lack of such anti-unitary operation. This study shows that non-symmorphic crystals with multiple fractional lattice translations exhibit rich topological properties.