Electronic correlations and competing orders in multiorbital dimers: a cluster DMFT study

TL;DR

This study uses cluster DMFT to explore how electronic correlations, Hund's coupling, and dimer formation influence magnetic and electronic phases in multiorbital transition metal oxides, revealing complex competing orders.

Contribution

It provides a detailed phase diagram of dimerized multiorbital oxides, highlighting the interplay of Hund's rule violation, dimerization, and electron correlations with novel magnetic states.

Findings

Identification of regimes as Fermi liquid, Peierls insulator, or strongly correlated states.

Observation of dimer-antiferromagnetic order with high-spin and low-spin states.

Discovery of an incoherent antiferromagnetic metal with local moments.

Abstract

We investigate the violation of the first Hund's rule in 4$d$ and 5$d$ transition metal oxides that form solids of dimers. Bonding states within these dimers reduce the magnetization of such materials. We parametrize the dimer formation with realistic hopping parameters and find not only regimes, where the system behaves as a Fermi liquid or as a Peierls insulator, but also strongly correlated regions due to Hund's coupling and its competition with the dimer formation. The electronic structure is investigated using the cluster dynamical mean-field theory for a dimer in the two-plane Bethe lattice with two orbitals per site and $3/8$-filling, that is three electrons per dimer. It reveals dimer-antiferromagnetic order of a high-spin (double exchange) state and a low-spin (molecular orbital) state. At the crossover region we observe the suppression of long-range magnetic order, fluctuation enhancement and renormalization of electron masses. At certain interaction strengths the system becomes an incoherent antiferromagnetic metal with well defined local moments.