Theory of electronic magnetoelectric coupling in $d^5$ Mott insulators

Abstract

Motivated by recent terahertz (THz) spectroscopy measurements in $\alpha$-RuCl${}_3$, we develop a theory for magnetoelectric (ME) effects in Mott insulators of $d^5$ transition metal ions in an octahedral crystal field. For $4d$ and $5d$ compounds, the relatively wide-spread orbitals favor charge fluctuations of localized electrons to neighboring ions and a significant ME effect from electronic mechanisms is expected. From a three-orbital Hubbard model with strong spin-orbit coupling, we derive the mechanisms for the electric polarization originating from virtual hopping of the localized holes carrying the spins. We consider the electric polarization generated by pairs of spin operators on nearest neighbor bonds with either an edge-sharing geometry (i.e., two ligands are shared) or a corner-sharing geometry (i.e., one ligand is shared). The allowed couplings are first derived using a symmetry approach. Then, we explicitly calculate the coupling constants and evaluate the effective polarization operator in the ground state manifold using perturbation theory and exact diagonalization. The results are relevant when considering the THz optical conductivity of magnetic systems such as some perovskite iridates or Kitaev materials. In particular, they help explain the recent THz optical measurements of $\alpha$-RuCl${}_3$ for which the electric-dipole-induced contribution has been shown to be strong.

arXiv comment20 pages, 6 figures

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Cited by in corpus (12)

• Cavity magnon-polaritons in cuprate parent compounds
• Magnetoelectric generation of a Majorana-Fermi surface in Kitaev's honeycomb model
• Optical excitation of magnons in an easy-plane antiferromagnet: Application to Sr${}_2$IrO${}_4$
• Electric probe for the toric code phase in Kitaev materials through the hyperfine interaction
• Tuning bulk topological magnon properties with light-induced magnons
• Discrete time crystal made of topological edge magnons
• Multipolar multiferroics in $4d^2$/$5d^2$ Mott insulators
• Evidence for distortion-induced local electric polarization in $\alpha$-RuCl${}_3$
• Electric polarization near vortices in the extended Kitaev model
• Real-time control of non-Abelian anyons in Kitaev spin liquid under energy dissipation
• Coupling of plasmons to the two-magnon continuum in antiferromagnets
• Tuning the Chern number of Kitaev quantum spin liquid