Electronic structures and topological properties in nickelates Ln n+1NinO2 n+2

After the significant discovery of the hole-doped nickelate compound Nd0.8Sr0.2NiO2, analyses of the electronic structure, orbital components, Fermi surfaces and band topology could be helpful to understand the mechanism of its superconductivity. Based on first-principle calculations, we find that Ni3d(x2-y2) states contribute the largest Fermi surface. The Ln5d(3z2-r2) states form an electron pocket at Gamma, while 5d(xy) states form a relatively bigger electron pocket at A. These Fermi surfaces and symmetry characteristics can be reproduced by our two-band model, which consists of two elementary band representations: B-1g@1a circle plus A(1g)@1b. We find that there is a band inversion near A, giving rise to a pair of Dirac points alongM-A below the Fermi level upon including spin-orbit coupling. Furthermore, we perform density functional theory based Gutzwiller (DFT+Gutzwiller) calculations to treat the strong correlation effect of Ni 3d orbitals. In particular, the bandwidth of 3d(x2-y2) has been renormalized largely. After the renormalization of the correlated bands, the Ni 3d(xy) states and the Dirac points become very close to the Fermi level. Thus, a hole pocket at A could be introduced by hole doping, which may be related to the observed sign change of the Hall coefficient. By introducing an additional Ni 3d(xy) orbital, the hole-pocket band and the band inversion can be captured in our modified model. Besides, the nontrivial band topology in the ferromagnetic two-layer compound La3Ni2O6 is discussed and the band inversion is associated with Ni 3d(x2-y2) and La 5d(xy) orbitals.