Electronic Structure of RNiC2 (R = La, Y, and Th)

The electronic structures of the non-centrosymmetric Ni-based superconductor LaNiC2, and related compounds YNiC2 and ThNiC2 are calculated by the full-potential augmented plane-wave method. In contrast to that in the case of other Ni-based superconductors, there is only one pair of Fermi surfaces taking the spin degree of freedom into account, when holes are slightly doped. The density of states at the Fermi level mainly consists of Ni 3d, but La 5d/Y 4d components are not negligible. Since their crystal structures lack the inversion symmetry, a spin-orbit interaction splits the bands. The splitting values are 3.1 and 2.0 mRy for LaNiC2 and YNiC2, respectively. Using the similarity of the band structures of LaNiC2 and ThNiC2, the Th4+ doping dependence of T-c for these compounds can be partly explained by an extended rigid band model.