Dimerization versus Orbital Moment Ordering in the Mott insulator YVO$_3$

TL;DR

This paper investigates the complex interplay of spin, orbital, and lattice effects in YVO$_3$, revealing a novel orbital moment ordering phase and explaining experimental magnetic phenomena through advanced theoretical modeling.

Contribution

It introduces a combined exact diagonalization and mean-field approach to uncover a new orbital ordering phase influenced by octahedral tilting in YVO$_3$.

Findings

Identification of a novel orbital moment ordered phase.

Explanation of spin canting and magnetization reduction.

Prediction of orbital Peierls instability and magnon splitting.

Abstract

We use exact diagonalization combined with mean-field theory to investigate the phase diagram of the spin-orbital model for cubic vanadates. The spin-orbit coupling competes with Hund's exchange and triggers a novel phase, with the ordering of $t_{2g}$ orbital magnetic moments stabilized by the tilting of VO$_6$ octahedra. It explains qualitatively spin canting and reduction of magnetization observed in YVO$_3$. At finite temperature an orbital Peierls instability in the $C$-type antiferromagnetic phase induces modulation of magnetic exchange constants even in absence of lattice distortions. The calculated spin structure factor shows a magnon splitting due to the orbital Peierls dimerization.