Carrier localization in correlated nickelates by electron doping

The electronic properties of transition metal oxides are often sensitive to the orbital occupancy of the \textit{3d} electrons due to non-degenerate energy levels and strong electron correlations. A prototypical rare earth nickelate, SmNiO$_{3}$ exhibits thermally driven insulator-metal transition at 400 K with one to two orders of magnitude change in its resistivity, characterized by charge ordering of the Ni sites. In this work, by modifying the $ e_{g}$ orbital filling of Ni through electron doping with reversible hydrogenation and lithium/magnesium intercalation, we realize a deep insulating phase with greater than eight orders of magnitude change in resistivity at room temperature. The band gap can be modulated by nearly 3 eV. We will consider the mechanisms leading to these striking observations in depth in this presentation.