Emergent flat-band physics in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>d</mml:mi><mml:mrow><mml:mn>9</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msup></mml:math> multilayer nickelates
Frank Lechermann
Abstract
Recent experiments showed that the reduced multilayer rare-earth (RE) nickel oxides of form $\mathrm{R}{\mathrm{E}}_{p+1}{\mathrm{Ni}}_{p}{\mathrm{O}}_{2p+2}$ may belong to the novel family of superconducting lanthanide nickelates. Here, the correlated electronic structure of ${\mathrm{Pr}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{8}$ and ${\mathrm{Nd}}_{6}{\mathrm{Ni}}_{5}{\mathrm{O}}_{12}$ is studied by means of an advanced realistic many-body framework. It is revealed that the low-energy physics of both systems is dominated by an interplay of Ni-${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and Ni-${d}_{{z}^{2}}$ degrees of freedom. While the Ni-${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbitals are always highly correlated near a (orbital-selective) Mott-insulating regime, the Ni-${d}_{{z}^{2}}$ orbitals give rise to intriguing nondispersive features. At low temperature, the Pr compound still displays quasiparticle-like Ni-${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-derived states at the Fermi level, but the interacting fermiology of the Nd compound is outshined by an emergent Ni-${d}_{{z}^{2}}$-controlling flat band. These findings translate well to the previous characterization of doped infinite-layer nickelates, and hence further make the case for a mechanism of unconventional superconductivity, which is distinct from the one in high-${T}_{\mathrm{c}}$ cuprates.