Excitonic Magnetism at the intersection of Spin-orbit coupling and crystal-field splitting

TL;DR

This paper investigates excitonic magnetism in strongly correlated, spin-orbit coupled materials, revealing its realization in Ca$_2$RuO$_4$ through theoretical modeling despite orbital polarization.

Contribution

It demonstrates the emergence of excitonic magnetism in a real material, Ca$_2$RuO$_4$, using ab-initio modeling and the Variational Cluster Approach.

Findings

Excitonic magnetism can coexist with orbital order and conventional antiferromagnetism.

Ca$_2$RuO$_4$ exhibits excitonic magnetism despite strong orbital polarization.

Theoretical methods successfully predict excitonic states in complex correlated materials.

Abstract

Excitonic magnetism involving superpositions of singlet and triplet states is expected to arise for two holes in strongly correlated and spin-orbit coupled $t_{2g}$ orbitals. However, uncontested material examples for its realization are rare. Applying the Variational Cluster Approach to the square lattice, we find conventional spin antiferromagnetism combined with orbital order at weak and excitonic order at strong spin-orbit coupling. We address the specific example of Ca$_2$RuO$_4$ using ab-initio modeling and conclude it to realize excitonic magnetism despite its pronounced orbital polarization.