Electronic Structures and the Spin-splittings in Ullmannite-type Structure Compounds

The electronic structure and the Fermi surfaces are investigated for iso-electronic compounds NiSbS and PdBiSe, based on the band structure calculations. A mineral ullmannite NiSbS belongs to the tetrahedral class T , which is the lowest symmetry class of the isometric (cubic) system and the space group is the same as MnSi. It is a non-symmorphic cubic chiral structure. Totally 4 hole and 4 electron Fermi surfaces are obtained, which are not degenerated by spin, due to the lack of the space inversion symmetry. The electronic band structure and the topology of the Fermi surfaces of both compounds are very similar, but the magnitudes of the splitting of the Fermi surfaces are quite different. The large spin-splitting in PdBiSe is mainly caused by the strong spin-orbit interaction of Bi 6p electrons.