Layer-resolved Electronic Structure and Correlation of Low-$n$ Square-planar Nickelates: A DFT+DMFT Prediction of Superconducting Candidates

Abstract

Multi-layer square-planar nickelates provide a rare platform in which the nominal Ni valence, dimensionality, and layer-resolved electronic structure can be tuned within the same structural family. Recent experiments have found superconductivity in $n=4$--8 $R_{n+1}Ni_nO_{2n+2}$ compounds, with the highest $T_c$ near $n=6$, whereas the more heavily hole-doped $n=3$ member remains nonsuperconducting. Here we propose spacer-layer Cl doping as a route to convert low-$n$ nickelates into superconducting candidates. Compared with changing the layer number $n$, Cl substitution on the spacer-layer oxygen sites offers a chemically natural way to continuously tune the Ni valence while leaving the NiO$_2$ planes largely intact; the lower-$n$ compounds may also be more accessible for synthesis. Using density functional theory combined with dynamical mean-field theory, we show that electron-compensated $n=2$ and $n=3$ La-based nickelates, targeted to the nominal Ni valence of superconducting $n=6$, develop Ni-$d$ correlations comparable to those of superconducting higher-$n$ compounds while preserving the characteristic low-energy Ni-$d$ electronic structure. These results suggest spacer-layer Cl doping as a promising strategy for designing low-$n$ square-planar nickelate superconductors.