Edge-sharing quasi-one-dimensional cuprate fragments in optimally substituted Cu/Pb apatite

TL;DR

This study investigates Cu-substituted lead apatite fragments, revealing the formation of edge-sharing Cu-O chains with antiferromagnetic order and intermediate electronic correlations, providing insights into potential strongly correlated physics in this material.

Contribution

It uncovers the formation of edge-sharing Cu-O chains in Cu-substituted apatite and analyzes their magnetic and electronic properties, highlighting controllable antiferromagnetism and low-dimensional behavior.

Findings

Formation of contiguous edge-sharing Cu-O chains.

Antiferromagnetic ground state near a ferromagnetic quantum critical point.

Electronic structure shows low-dimensional, intermediate correlated regime.

Abstract

The flurry of theoretical and experimental studies following the report of room-temperature superconductivity at ambient pressure in Cu-substituted lead apatite Cu$_x$Pb$_{10-x}$(PO$_4$)$_6$O (`LK99') have explored whether and how this system might host strongly correlated physics including superconductivity. While first-principles calculations at low doping ($x\approx1$) have indicated a Cu-$d^{9}$ configuration coordinated with oxygen giving rise to isolated, correlated bands, its other structural, electronic, and magnetic properties diverge significantly from those of other known cuprate systems. Here we find that higher densities of ordered Cu substitutions can result in the formation of contiguous edge-sharing Cu-O chains, akin to those found in some members of the cuprate superconductor family. Interestingly, while such quasi-one-dimensional edge-sharing chains are typically ferromagnetically coupled along the chain, we find an antiferromagnetic ground-state magnetic order for our cuprate fragments which is in proximity to a ferromagnetic quantum critical point. This is a result of the elongated Cu-Cu distance in Cu-substituted apatite that leads to larger Cu-O-Cu angles supporting antiferromagnetism, which we demonstrate to be controllable by strain. Finally, our electronic structure calculations confirm the low-dimensional nature of the system and show that the bandwidth is driven by the Cu-O plaquette connectivity, resulting in an intermediate correlated regime.