Electronic structure of NdNiO[formula omitted] superconductor from ab initio density-functional-theory calculations

Abstract

Understanding high-temperature superconductivity is nowadays a challenge in the area of quantum materials and presents major unsolved problems. The recent discovery of superconductivity in infinite-layer nickelates has provided a new platform for studying unconventional superconductivity. Although the nickelates are analogous to the cuprates high-temperature superconductors, many theoretical analyses indicate that the nickelates do not precisely mirror the cuprates. For instance, hybridization between Ni 3dx2−y2 and O 2p is weak, which presents a high contrast to the hybridization between Cu 3d and O 2p in the cuprates. The similarities and differences between the nickelates and the cuprates provide great opportunities to reveal the origin of high-temperature superconductivity. In this study, with the employment of first-principles density-functional-theory calculations, we determine and analyze the electronic structure of the undoped infinite-layer nickelate NdNiO2. By performing phonon calculations and estimating the strength of the electron–phonon coupling, we find that this latter is weak, which indicates that the conventional BCS theory alone cannot explain the observed superconductivity in this material. Consequently, other still-unknown mechanisms may be at play. Moreover, we show from electronic band calculations that another conduction band crosses the Fermi level in addition to the Ni 3dx2−y2 band. This non-Ni conduction electron band is mainly composed of three orbitals: Nd 5d3z2−r2, Nd 5dxy, and another s-like orbital that does not belong to any specific atom. This interstitial s-like orbital is located around the (0,0,0.5) site. The rare-earth orbital Nd 5d3z2−r2 mixes with Ni 3dx2−y2 at the Fermi level, which causes some holes from the Nd 5d band to be (self-) doped into the Ni 3dx2−y2 orbitals.