Abstract
Motivated by the recently reported high-temperature superconductivity in the bilayer La3Ni2O7 (LNO) under pressure, here 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 d3z2−r2 orbitals form a bonding-antibonding molecular orbital state via the O pz inducing a “dimer” lattice in the LNO bilayers. The Fermi surface consists of two-electron sheets with mixed eg orbitals and a hole pocket defined by the d3z2−r2 orbital, suggesting a Ni two-orbital minimum model. Different from the infinite-layer nickelate, we obtained a large interorbital hopping between d3z2−r2 and dx2−y2 states in LNO, caused by the ligand “bridge” of in-plane O px or py 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.
