Mimicking cuprates: large orbital polarization in a metallic square-planar nickelate

TL;DR

This study identifies Pr4Ni3O8 as a promising cuprate analog with metallic behavior and cuprate-like electronic structure, offering new insights into high-temperature superconductivity research.

Contribution

It reports the discovery of a metallic, low-spin, orbitally polarized nickelate with cuprate-like electronic features, advancing the search for high-Tc superconductor analogs.

Findings

Pr4Ni3O8 avoids charge-stripe order and is metallic.

Exhibits significant orbital polarization with dx2-y2 character.

Closest known analog to cuprates in 3d electron count.

Abstract

High temperature cuprate superconductivity remains a defining problem in condensed matter physics. Among myriad approaches to addressing this problem has been the study of alternative transition metal oxides with similar structures and 3d electron count that are suggested as proxies for cuprate physics. None of these analogs has been superconducting, and few are even metallic. Here, we report that the low-valent, quasi-two-dimensional trilayer compound, Pr4Ni3O8 avoids a charge-stripe ordered phase previously reported for La4Ni3O8, leading to a metallic ground state. By combining x-ray absorption spectroscopy and density functional theory calculations, we further find that metallic Pr4Ni3O8 exhibits a low-spin configuration and significant orbital polarization of the unoccupied eg states with pronounced dx2-y2 character near the Fermi energy, both hallmarks of the cuprate superconductors. Belonging to a regime of 3d electron count found for hole-doped cuprates, Pr4Ni3O8 thus represents one of the closest analogies to cuprates yet reported and a singularly promising candidate for high-Tc superconductivity if appropriately doped.