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.

Automated summary

The electronic structure and band topology of Nd0.8Sr0.2NiO2 were analyzed to understand its superconductivity mechanism, revealing characteristics such as the largest Fermi surface contribution from Ni3d(x2-y2) states. The band inversion near A points and the impact of strong correlation effects on Ni 3d orbitals were also discussed in relation to the observed sign change of the Hall coefficient.