Electronically highly cubic conditions for Ru in α−RuCl3

Abstract

We studied the local Ru 4d electronic structure of α-RuCl3 by means of polarization dependent xray absorption spectroscopy at the Ru-L2,3 edges. We observed a vanishingly small linear dichroism indicating that electronically the Ru 4d local symmetry is highly cubic. Using full multiplet cluster calculations we were able to reproduce the spectra excellently and to extract that the trigonal splitting of the t2g orbitals is −12 ± 10 meV, i.e. negligible as compared to the Ru 4d spin-orbit coupling constant. Consistent with our magnetic circular dichroism measurements, we found that the ratio of the orbital and spin moments is 2.0, the value expected for a J eff = 1/2 ground state. We have thus shown that as far as the Ru 4d local properties are concerned, α-RuCl3 is an ideal candidate for the realization of Kitaev physics.Geometrically frustrated quantum spin systems are important owing to the fact that frustration often results in a suppression of conventional mean field ground states in favor of more exotic phases of matter. Current research focuses on the effect of spin-orbit coupling (SOC) and the role it plays in the realization of different exotic phases such as unconventional superconductivity or quantum spin liquids [1-3]. Especially, quantum spin liquids can result in topological states with fractional excitations. An important, theoretically solvable model is the Kitaev model with spin-1/2 on a honeycomb lattice, where the coupling between neighboring spins is highly anisotropic with bond-dependent spin interactions. In contrast to spin liquids arising from usual geometrical frustrated spin arrangements, the bond-dependent spin interactions within the Kitaev model frustrate the spin configuration on a single site [4].The search for fractionalized excitations and the identification of a Kitaev spin liquid state has been experimentally quite difficult. Increased attention has been focussed on the honeycomb iridates [5,6], starting from the assumption that large spin-orbit coupling is the leading energy scale in determining the ground state such that the Ir 5d t 2g orbitals are described in terms of J eff = 1/2 and 3/2 orbitals. However, the real iridate systems exhibit trigonal distortion (D trig = 0.1 eV [6]) and a significant itinerant character of the Ir 5d orbitals [7-9], which complicates the electronic ground state. Despite a flurry of both theoretical and experimental studies, the nature of the ground state in honeycomb iridates are being fiercely debated and the occurrence of Kitaev physics is still far from clear.Recently, α-RuCl 3 has been suggested as a promising candidate material for the realization of the Kitaev model [10] and excitations observed via Raman [11,12] and in-elastic neutron scattering [13] have been presented as evidence that α-RuCl 3 may be close to a quantum spin liquid ground state. In the last two years a number of publications discussing the realization of the Kitaev physics in α-RuCl 3 has appeared in literature [3,[14][15][16][17][18][20][21][22][23][24][25][26][27][28][29]...

Magnetic Excitations and Continuum of a Possibly Field-Induced Quantum Spin Liquid in α−RuCl3

“…The linear opening of the spin gap is a feature expected for models beyond the Kitaev limit [37]. The apparent g * -factor revealed here is significantly larger than the value of g ab = 2.5 estimated from the magnetization measurements [11] or g ab = 2.27 from the x-ray magnetic circular dichroism experiments [38], which is a reminiscence of the existence of bound states and many-body interactions in the QSL, as for the Heisenberg spin-1/2 chains [39,40].…”

Comparative Study of Potentially Jeff = 0 Ground State Iridium(V) in SrLaNiIrO6, SrLaMgIrO6, and SrLaZnIrO6

“…To analyze the results quantitatively, we need to make a theoretical estimate for the effective magnetic moments for the Ni and Ir ions. To this end we resort to configuration interaction cluster model calculations, an approach which is very successful to explain quantitatively the basic local electronic and magnetic properties of a wide range of insulating transition metal oxides . This model includes the full atomic multiplet theory and takes into account the intra‐atomic transition metal d–d Coulomb interactions, the atomic d spin‐orbit coupling, the O2p to transition metal d hybridization, and the local ionic crystal field parameters .…”

Ferromagnetic Kitaev interaction and the origin of large magnetic anisotropy in α-RuCl3

“…A conventional way to explain this would be resorting to the g-factor anisotropy. However, experimental data suggest that g-factor anisotropy cannot be very large, certainly not large enough to account for the anisotropic susceptibility [28,29]. Another route to obtain a large magnetic anisotropy is via a large Γ term as suggested in Ref.…”