Orbital disorder induced by charge fluctuations in vanadium spinels

TL;DR

This paper investigates how charge fluctuations in vanadium spinels cause orbital disorder, especially as electronic delocalization increases with smaller cation sizes, revealing a crossover from ordered to disordered orbital states.

Contribution

It analyzes the evolution of orbital ordering in vanadium spinels across different coupling regimes using a multi-orbital Hubbard model, highlighting the role of magnetic ordering and charge fluctuations.

Findings

Orbital order diminishes with increased charge fluctuations.

Charge fluctuations are enhanced along ferromagnetic bonds.

System transitions from strong to intermediate-coupling regimes.

Abstract

Motivated by recent experiments on vanadium spinels, $A$V$_2$O$_4$, that show an increasing degree of electronic delocalization for smaller cation sizes, we study the evolution of orbital ordering (OO) between the strong and intermediate-coupling regimes of a multi-orbital Hubbard Hamiltonian. The underlying magnetic ordering of the Mott insulating state leads to a rapid suppression of OO due to enhanced charge fluctuations along ferromagnetic bonds. Orbital double-occupancy is rather low at the transition point indicating that the system is in the crossover region between strong and intermediate-coupling regimes when the orbital degrees of freedom become disordered.