Exploring d-Wave Magnetism in Cuprates from Oxygen Moments

TL;DR

This paper investigates how doping-induced oxygen magnetic moments in cuprates can lead to unconventional d-wave altermagnetic states, expanding understanding of magnetic phenomena beyond copper moments.

Contribution

It introduces a new mechanism for altermagnetism in cuprates driven by oxygen moments without crystal symmetry breaking, supported by theoretical and computational analysis.

Findings

Identification of oxygen-based altermagnetic states in cuprates.

Demonstration of conditions for oxygen AM formation via Hartree-Fock and exact diagonalization.

Proposal of a candidate compound and experimental implications for oxygen AM.

Abstract

The antiferromagnetic parent phase of high-T$_c$ cuprates has been established as a N\'eel state of copper moments, but early work pointed out the important role of ligand oxygen orbitals. Using the three-orbital Emery model, we explore how, and under which conditions, doping-induced antiferromagnetic ordering of weak magnetic moments on the oxygen sites can lead to unconventional d-wave magnetism with spin-split electronic bands. The mechanism for forming such altermagnetic (AM) states in cuprates does not rely on a lowering of the crystal symmetry but rather on interaction-induced formation of magnetic moments on directional oxygen orbitals within the crystallographic unit cell. Therefore, we obtain two different types of AM, namely a (0,0)-AM and a ($\pi$,$\pi$)-AM. We explore different regimes and challenges for realizing oxygen AM supported by Hartree-Fock calculations and complementary exact diagonalization of small clusters. While the region of interacting parameters needed to realize these states may be difficult to achieve in known high-T$_c$ cuprates, we propose a scenario to realize AM induced by oxygen magnetic moments in a cuprate-based candidate compound using density functional theory and discuss experimental implications.