Excitonic magnetism in $d^6$ perovskites

TL;DR

This study investigates the potential for exciton condensation in $d^6$ perovskites like LaCoO$_3$, revealing conditions that favor or suppress excitonic magnetic order through computational modeling.

Contribution

The paper demonstrates the possibility of excitonic magnetism in $d^6$ perovskites using LDA+U calculations and analyzes how structural distortions and spin-orbit coupling influence this phenomenon.

Findings

Multiple solutions with spin-triplet exciton condensate found

Rhombohedral distortion suppresses excitonic order

Spin-orbit coupling enhances excitonic condensation energy

Abstract

We use the LDA+U method to study the possibility of exciton condensation in perovskites of transition metals with $d^6$ electronic configuration such as LaCoO$_3$. For realistic interaction parameters we find several distinct solutions exhibiting spin-triplet exciton condensate, which gives rise to a local spin density distribution while the ordered moments are vanishingly small. Rhombohedral distortion from the ideal cubic structure suppresses the ordered state, contrary to the spin-orbit coupling which enhances the excitonic condensation energy. We explain the trends observed in the numerical simulations with the help of a simplified strong-coupling model. Our results indicate that LaCoO$_3$ is close to the excitonic instability and suggest ways to make it order.