Reentrant behavior of metal-insulator transition in AgCo_xNi_1-xO₂ (0.33 ≤ x ≤ 0.66) delafossite : DFT+U and Quantum Monte Carlo Study

As the only semimetallic d¹⁰-based delafossite, AgNiO₂ has received a great deal of attention due to both its unique semimetallicity and its antiferromagnetism in the NiO₂ layer that is coupled with a lattice distortion. In contrast, other delafossites such as AgCoO₂ are insulating. Here we study how the electronic structure of AgCo_xNi_1-xO₂ alloys vary with Ni/Co concentration, in order to investigate the electronic properties and phase stability of the intermetallics. In order to treat strong on-site Coulomb interactions accurately, in this study we use Quantum Monte Carlo (QMC) simulations to obtain accurate estimates for the electronic and magnetic properties of AgNiO₂. By comparison to Density Functional Theory (DFT) results, we show that strong electron correlations in NiO₂ layer are critical to account for. We show that Co doping on the magnetic Ni sites results in a metal-insulator transition near x ~ 0.33, which is consistent with the experimental result. In addition, we observe the reentrance to the metallic phase on high Co concentration near x ~ 0.66.