Electronic properties of hydrogen-doped square-planar nickelates

The layered square-planar nickelates Rₙ₊₁NiₙO₂ₙ₊₂ (R: rare-earth element) hold great promise in realizing cupratelike superconductors. While the appearance of zero resistivity is extremely sensitive to the concentration of hydrogen(x) in infinite-layer Sr0.2Nd0.8NiO₂Hₓ, the configurations of many other Ndₙ₊₁NiₙO₂ₙ₊₂Hₓ and the general roles of H in these systems are still unknown. Using first-principles calculations, we find that H atoms prefer to form staggered one-dimensional chains along the c axis, which are obstructed by the fluorite layer of Ndₙ₊₁NiₙO₂ₙ₊₂. Importantly, the charge-transfer energy between O $2p$ and Ni $3d$, one of the key factors determining the superconducting temperature in cuprates, is largely and continuously tunable by n and x in nickelates. Further, from the perspective of orbital hybridization and orbital polarization, the quasi-two-dimensional electronic properties are more pronounced for nickelates with smaller n, potentially facilitating superconductivity. These findings shed light on the general roles of H in controlling electronic properties in nickelates and provide valuable guidance for the experimental preparation of superconducting Rₙ₊₁NiₙO₂ₙ₊₂ materials.