Covalency-driven unusual metal-insulator transition in nickelates

Abstract

Electronic structures of metallic ${\mathrm{LaNiO}}_3$ and insulating ${\mathrm{NdNiO}}_3$ are investigated using electron spectroscopies as well as band-structure and model-Hamiltonian calculations. It is shown that there is an increase in the transfer integral, ${\mathit{t}}_{\mathit{p}\mathit{d}}$ in ${\mathrm{LaNiO}}_3$ compared to ${\mathrm{NdNiO}}_3$ though ${\mathit{U}}_{\mathit{d}\mathit{d}}$ and Δ are very similar. A phase diagram obtained with a multiband Hubbard model explains the metal-insulator transition as well as the anomalous resistivity of ${\mathrm{NdNiO}}_3$ under pressure while indicating various interesting possibilities near the metal-insulator phase line.