On the nature of the magnetic ground-state wave function of V$_2$O$_3$

TL;DR

This paper critically examines conflicting experimental interpretations of V$_2$O$_3$'s magnetic ground state, discusses the limitations of LDA+U, and proposes symmetry-based explanations for the magnetic moment orientation.

Contribution

It clarifies the magnetic structure of V$_2$O$_3$, critiques existing experimental interpretations, and suggests new tests and theoretical insights into the ground-state wave function.

Findings

Identifies conflicts in experimental interpretations of magnetic symmetry.

Highlights limitations of LDA+U due to non-local correlations.

Provides symmetry-based explanation for magnetic moment orientation.

Abstract

After a brief historical introduction, we dwell on two recent experiments in the low-temperature, monoclinic phase of V$_2$O$_3$: K-edge resonant x-ray scattering and non-reciprocal linear dichroism, whose interpretations are in conflict, as they require incompatible magnetic space groups. Such a conflict is critically reviewed, in the light of the present literature, and new experimental tests are suggested, in order to determine unambiguously the magnetic group. We then focus on the correlated, non-local nature of the ground-state wave function, that is at the basis of some drawbacks of the LDA+U approach: we singled out the physical mechanism that makes LDA+U unreliable, and indicate the way out for a possible remedy. Finally we explain, by means of a symmetry argument related to the molecular wave function, why the magnetic moment lies in the glide plane, even in the absence of any local symmetry at vanadium sites.