Exploring the 4d¹ analogue of cuprates: theoretical studies on bulk NbF₄ and NbF₄ monolayer stabilized on MgO (001) plane

Abstract The recent research in infinite-layer nickelates has inspired new effort in finding the cuprate analogs. Here we propose that NbF4, which contains niobium-centered fluorine octahedra, is a promising 4d 1 analogue of cuprates. Using the density functional theory, we first show that bulk NbF4 is in close proximity to d 1 configuration, with Nb 4 d x y orbital nearly half-filled. A single band with dominating 4 d x y character crosses the Fermi level, forming a square-like Fermi surface. The intralayer G-type antiferromagnetic (AFM) order is energetically favored and the Coulomb interaction drives the system into an AFM insulator. Next we demonstrate that the NbF4 layer can be stabilized on MgO substrate with main electronic and magnetic features retained, offering an alternative route to realize the NbF4-related high-T c superconductors. Furthermore, we derive effective single orbital models for both systems and investigate the electron correlation effects via functional renormalization group. We find that the G-type AFM dominates near half-filling but d x 2 − y 2 -wave superconductivity (SC) prevails upon suitable hole/electron doping. Based on the striking similarities between NbF4 and cuprates, we suggest that NbF4-related compounds may be exotic candidates for searching new high-T c superconductors.