Origin of the transitions inversion in rare-earth vanadates

TL;DR

This paper explains the unusual inversion of orbital and magnetic transition temperatures in RVO3 rare-earth vanadates by revealing a hierarchy of interactions through advanced theoretical modeling.

Contribution

It introduces a novel theoretical framework combining dynamical mean-field theory with tensor decomposition to explain the transition inversion phenomenon.

Findings

Orbital physics controlled by quadrupolar super-exchange rather than lattice distortion.

Competing spin super-exchange interactions lead to early magnetic order.

Criteria established for identifying similar behavior in other materials.

Abstract

The surprising inversion of the orbital- and magnetic-order transition temperatures in the RVO3 series with increasing the rare-earth radius makes the series unique among orbitally-ordered materials. Here, augmenting dynamical mean-field theory with a decomposition of the order parameter into irreducible tensors, we show that this anomalous behavior emerges from an unusual hierarchy of interactions. First, increasing the rare-earth radius, orbital physics comes to be controlled by xz-xz quadrupolar super-exchange rather than by lattice distortion. Next, for antiferromagnetic spin order, orbital super-exchange terms with different spin rank compete, so that the dipolar spin-spin interaction dominates. Eventually, G-type magnetic order (anti-ferro in all directions) can appear already above the orbital ordering transition, and C-type order (anti-ferro in the ab plane) right around it. The strict constraints we found explain why the inversion is rare, giving at the same time criteria to look for similar behavior in other materials.