Superconducting phase diagram of multi-layer square-planar nickelates

TL;DR

This study maps the phase diagram of multi-layer square-planar nickelates, revealing superconductivity in certain layers, and highlights their similarities and differences with cuprates, advancing the understanding of nickel-based superconductors.

Contribution

It constructs a comprehensive phase diagram for multi-layer nickelates and uncovers superconductivity signatures in layers with n=4-8, showing structural and electronic similarities to cuprates.

Findings

Superconductivity observed for n=4-8 layers.

Superconducting anisotropy varies with dimensionality.

Electronic structure approaches cuprate-like behavior.

Abstract

The discovery of superconductivity in square-planar nickelates has offered a rich materials platform to explore the origins of cuprate-like superconductivity. Experimental investigations however have largely been limited to the infinite-layer $R$NiO$_2$ ($R$=rare-earth) nickelates. Here, we construct a phase diagram of multi-layer square-planar Nd$_{n+1}$Ni$_n$O$_{2n+2}$ compounds and discover signatures of superconductivity for $n$ = 4 - 8. Upon decreasing the dimensionality $n$, the superconducting anisotropy evolves due to 4$f$ electron effects, and electronic structure characteristics approach cuprate-like behavior. Magnetic fluctuations persist from within the superconducting regime and into the over-doped, non-superconducting regime. Remarkably, the superconducting regime overlaps with that of chemically-doped infinite-layer nickelates, demonstrating underlying commonalities and distinct differences across varying structural realizations of square-planar nickelates. Our work establishes this layered template for creating new nickel-based superconductors.