Electronic structure, dimer physics, orbital-selective behavior, and magnetic tendencies in the bilayer nickelate superconductor $\mathrm{La_3Ni_2O_7}$under pressure
Motivated by the recently reported high-temperature superconductivity in the bilayer La 3 Ni 2 O 7 (LNO) under pressure, we comprehensively study this system using ab initio techniques. The Ni 3d orbitals have a large bandwidth at ambient pressure, increasing by ~22% at 29.5 GPa. Without electronic interactions, the Ni d 3z 2 -r 2 orbitals form a bonding-antibonding molecular orbital state via the O p z inducing a “dimer” lattice in the LNO bilayers. The Fermi surface consists of two-electron sheets with mixed e g orbitals and a hole pocket defined by the d 3z 2 -r 2 orbital, suggesting a Ni two-orbital minimum model. Different from the infinite-layer nickelate, we obtained a large interorbital hopping between d 3z 2 -r 2 and d x 2 -y 2 states in LNO, caused by the ligand “bridge” of in-plane O p x or p y orbitals connecting those two orbitals, inducing d-p σ-bonding characteristics. The competition between the intraorbital and interorbital hoppings leads to an interesting dominant spin stripe (π,0) order because of bond ferromagnetic tendencies via the recently discussed “half-empty” mechanism.