Topotactic Hydrogen in Nickelate Superconductors and Akin Infinite-Layer Oxides <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi><mml:mi>B</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Liang Si, Wen Xiao, Josef Kaufmann, Jan M. Tomczak, Yi Lu, Zhicheng Zhong, Karsten Held
Abstract
Superconducting nickelates appear to be difficult to synthesize. Since the chemical reduction of $AB{\mathrm{O}}_{3}$ [rare earth ($A$), transition metal ($B$)] with ${\mathrm{CaH}}_{2}$ may result in both $AB{\mathrm{O}}_{2}$ and $AB{\mathrm{O}}_{2}\mathrm{H}$, we calculate the topotactic H binding energy by density functional theory (DFT). We find intercalating H to be energetically favorable for ${\mathrm{LaNiO}}_{2}$ but not for Sr-doped ${\mathrm{NdNiO}}_{2}$. This has dramatic consequences for the electronic structure as determined by $\mathrm{DFT}+\mathrm{dynamical}$ mean field theory: that of $3{d}^{9}$ ${\mathrm{LaNiO}}_{2}$ is similar to (doped) cuprates, $3{d}^{8}$ ${\mathrm{LaNiO}}_{2}\mathrm{H}$ is a two-orbital Mott insulator. Topotactic H might hence explain why some nickelates are superconducting and others are not.