The electronic structure and disorder effect of La$_3$Ni$_2$O$_{7}$ superconductor

TL;DR

This paper investigates the electronic structure of La$_3$Ni$_2$O$_7$ under high pressure, emphasizing the role of apical oxygens and disorder effects, and proposes a minimal two-orbital model relevant to its superconductivity.

Contribution

It provides a more accurate electronic structure of La$_3$Ni$_2$O$_7$ using hybrid functionals and analyzes the impact of apical oxygen vacancies on its Fermi surface and potential superconductivity.

Findings

Binding $d_{z^2}$ band is below Fermi level at high pressure.

Antisymmetric electronic structure is highly entangled.

Oxygen vacancies can suppress superconductivity by destroying the Fermi surface.

Abstract

Determining the electronic structure of La$_3$Ni$_2$O$_7$ is an essential step towards uncovering their superconducting mechanism. It is widely believed that the bilayer apical oxygens play an important role in the bilayer La$_3$Ni$_2$O$_7$ electronic structure. Applying the hybrid exchange-correlation functionals, we obtain a more accurate electronic structure of La$_3$Ni$_2$O$_7$ at its high-pressure phase, where the binding $d_{z^2}$ band is below the Fermi level owing to apical oxygen. The symmetry properties of this electronic structure and its corresponding tight-binding model are further analyzed. We find the antisymmetric part is highly entangled leading to a minimal nearly degenerate two-orbital model. Then, the apical oxygen vacancies effect is studied using the dynamical cluster approximation. This disorder effect strongly destroys the antisymmetric $\beta$ Fermi surface leading to the possible disappearance of superconductivity.