Fermi-level Dirac crossings in 4d and 5d cubic metal oxides: NaPd3 O4 and NaPt3 O4

The cubic oxide metals NaM3O4 (M=Pd or Pt) crystallize in the nonsymmorphic Pm3ąn space group. First-principles calculations are employed here to understand the role of the MO4 square planes and M-M interactions in the development of the electronic structure. The compounds host numerous Dirac crossings near the Fermi level which, in the absence of spin-orbit coupling, appear to form a cubic nodal state. Spin-orbit coupling fragments this nodal state into smaller regions with Dirac-like character, with the fragmenting being more pronounced in the M=Pt compound.