Quantum magnets with spin J = 2, which arise in spin-orbit coupled Mott insulators, can potentially display multipolar orders. Motivated by gaining a better microscopic understanding of the local physics of such d-orbital quantum magnets, we carry out an exact diagonalization study of a simple octahedral crystal field Hamiltonian for two electrons, incorporating spin-orbit coupling (SOC) and interactions. While the rotationally invariant Kanamori interaction in the t2g sector leads to a five-fold degenerate J = 2 manifold, we find that either explicitly including the eg orbitals, or going beyond the rotationally invariant Coulomb interaction within the t2g sector, causes a degeneracy breaking of the J = 2 levels. This can lead to a low-lying non-Kramers doublet carrying quadrupolar and octupolar moments and an excited triplet which supports magnetic dipole moments, bolstering our previous phenomenological proposal for the stabilization of ferro-octupolar order in heavy transition metal oxides. We show that the spontaneous time-reversal symmetry breaking due to ferro-octupolar ordering within the non-Kramers doublet leads to electronic orbital loop currents. The resulting internal magnetic fields can potentially explain the small fields inferred from muon-spin relaxation (µSR) experiments on cubic 5d 2 osmate double perovskites Ba2ZnOsO6, Ba2CaOsO6, and Ba2MgOsO6, which were previously attributed to weak dipolar magnetism. We make further predictions for oxygen NMR experiments on these materials. We also study the reversed level scheme, where the J = 2 multiplet splits into a low-lying magnetic triplet and excited non-Kramers doublet, presenting single-ion results for the magnetic susceptibility in this case, and pointing out its possible relevance for the rhenate Ba2YReO6. Our work highlights the intimate connection between the physics of heavy transition metal oxides and that of f -electron based heavy fermion compounds.PACS numbers: 75.25.aj, 75.40.Gb, 75.70.Tj Multipolar orders have been proposed and discussed extensively in f -orbital based heavy fermion compounds 1-14 . Such multipolar orders have also been proposed to occur in d-orbital metals with large spinorbit coupling (SOC), such as LiOsO 3 and Cd 2 Re 2 O 7 , via Pomeranchuk instabilities of the Fermi liquid 15 . Optical second-harmonic generation experiments on Cd 2 Re 2 O 7 have found evidence for such an inversion broken quadrupolar ordered state below T c ∼ 200 K 16 . Other candidates for multipolar orders include proposed quadrupolar order in A 2 OsO 4 (with A = K,Rb,Cs) 17 .In recent work, we have studied d-orbital Mott insulators with large SOC and a d 2 configuration in a local octahedral environment, and proposed these systems as candidates for realizing ferro-octupolar order 18,19 . Previous studies of such d 2 quantum magnets 20-22 have argued that the combination of crystal field and interaction effects, leads to the stabilization of a state with total L = 1 and S = 1, which are locked by SOC into a J = 2 spin. Motivated by experiments ...
The quest for exotic quantum magnetic ground states, including the Kitaev spin liquid and quantum spin-ices, has led to the discovery of several quantum materials where low energy pseudospin-1/2 doublets arise from the splitting of spin-orbit entangled multiplets with higher degeneracy. Such systems include d-orbital and f -orbital Mott insulators. When the gap between the low energy pseudospin-1/2 levels and the excited levels of the multiplet or 'excitons' is not large, the effective low-energy exchange interactions between the low energy pseudospin-1/2 moments can acquire significant corrections from coupling to the excitons. We extract these corrections using higher order perturbation theory as well as an exact Schrieffer-Wolff transformation. Such corrections can impact the exchange matrix for the low energy pseudospin-1/2 levels by renormalizing the strength and the sign of Heisenberg exchange or Ising anisotropies, and potentially even inducing bond-anisotropic couplings such as Kitaev-Γ exchange interactions. We discuss recent experiments on various cobaltate and osmate materials which hint at the ubiquity and importance of this physics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.