Spin-Orbit-Lattice Entangled State in A_{2}MgReO_{6} (A=Ca, Sr, Ba) Revealed by Resonant Inelastic X-Ray Scattering.

The 5d^{1} ordered double perovskites present an exotic playground for studying novel multipolar physics due to large spin-orbit coupling. We present Re L_{3} edge resonant inelastic x-ray scattering (RIXS) results that reveal the presence of the dynamic Jahn-Teller effect in the A_{2}MgReO_{6} (A=Ca, Sr, Ba) family of 5d^{1} double perovskites. The spin-orbit excitations in these materials show a strongly asymmetric line shape and exhibit substantial temperature dependence, indicating that they are dressed with lattice vibrations.

Resonating holes vs molecular spin-orbit coupled states in group-5 lacunar spinels.

The valence electronic structure of magnetic centers is one of the factors that determines the characteristics of a magnet. This may refer to orbital degeneracy, as for j = 1/2 Kitaev magnets, or near-degeneracy, e.g.

Dressed j-1/2 objects in mixed-valence lacunar spinel molybdates.

The lacunar-spinel chalcogenides exhibit magnetic centers in the form of transition-metal tetrahedra. On the basis of density-functional computations, the electronic ground state of an Mo tetrahedron has been postulated as single-configuration a e t, where a, e, and t are symmetry-adapted linear combinations of single-site Mo t atomic orbitals. Here we unveil the many-body tetramer wave-function: we show that sizable correlations yield a weight of only 62% for the a e t configuration.

How Correlations and Spin-Orbit Coupling Work within Extended Orbitals of Transition-Metal Tetrahedra of 4d/5d Lacunar Spinels.

Spin-orbit quartet ground states are associated with rich phenomenology, ranging from multipolar phases in f rare-earth borides to magnetism emerging through covalency and vibronic couplings in d transition-metal compounds. The latter effect has been studied since the 1960s on t octahedral units in both molecular complexes and extended solid-state lattices. Here we analyze the = 3/2 quartet ground state of larger cubane-like entities in lacunar spinels, composed of transition-metal () tetrahedra caged by chalcogenide ligands ().

Terahertz Magneto-Optical Excitations of the sd-Hybrid States of Lithium Nitridocobaltate Li(LiCo)N.

We report the results of the experimental and theoretical study of the magnetic anisotropy of single crystals of the Co-doped lithium nitride Li(LiCo)N with = 0.005, 0.01, and 0.

Engineering Kitaev exchange in stacked iridate layers: impact of inter-layer species on in-plane magnetism.

Novel functionalities may be achieved in oxide electronics by appropriate stacking of planar oxide layers of different metallic species, MO and M'O . The simplest mechanism allowing the tailoring of the electronic states and physical properties of such heterostructures is of electrostatic nature-charge imbalance between the M and M' cations. Here we clarify the effect of interlayer electrostatics on the anisotropic Kitaev exchange in HLiIrO, a recently proposed realization of the Kitaev spin liquid.

Strong Effect of Hydrogen Order on Magnetic Kitaev Interactions in H_{3}LiIr_{2}O_{6}.

Very recently a quantum liquid was reported to form in H_{3}LiIr_{2}O_{6}, an iridate proposed to be a close realization of the Kitaev honeycomb model. To test this assertion we perform detailed quantum chemistry calculations to determine the magnetic interactions between Ir moments. We find that weakly bond dependent ferromagnetic Kitaev exchange dominates over other couplings, but still is substantially lower than in Na_{2}IrO_{3}.

Selective arc-discharge synthesis of DyS-clusterfullerenes and their isomer-dependent single molecule magnetism.

A method for the selective synthesis of sulfide clusterfullerenes DyS@C is developed. Addition of methane to the reactive atmosphere reduces the formation of empty fullerenes in the arc-discharge synthesis, whereas the use of DyS as a source of metal and sulfur affords sulfide clusterfullerenes as the main fullerene products along with smaller amounts of carbide clusterfullerenes. Two isomers of DyS@C with (6) and (8) cage symmetry, DyS@C-(10528), and a carbide clusterfullerene DyC@C-(6) were isolated.

Spin-reversal energy barriers of 305 K for Fe d ions with linear ligand coordination.

A remarkably large magnetic anisotropy energy of 305 K is computed by quantum chemistry methods for divalent Fe d substitutes at Li-ion sites with D point-group symmetry within the solid-state matrix of LiN. This is similar to values calculated by the same approach and confirmed experimentally for linearly coordinated monovalent Fe d species, among the largest so far in the research area of single-molecule magnets. Our ab initio results therefore mark a new exciting exploration path in the search for superior single-molecule magnets, rooted in the configuration of d transition-metal ions with linear or quasilinear nearest-neighbor coordination.

Kitaev exchange and field-induced quantum spin-liquid states in honeycomb α-RuCl.

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d honeycomb halide α-RuCl.

Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods.

In existing theoretical approaches to core-level excitations of transition-metal ions in solids relaxation and polarization effects due to the inner core hole are often ignored or described phenomenologically. Here we set up an ab initio computational scheme that explicitly accounts for such physics in the calculation of x-ray absorption and resonant inelastic x-ray scattering spectra. Good agreement is found with experimental transition-metal L-edge data for the strongly correlated d cuprate LiCuO, for which we determine the absolute scattering intensities.

The vicinity of hyper-honeycomb β-Li2IrO3 to a three-dimensional Kitaev spin liquid state.

Due to the combination of a substantial spin-orbit coupling and correlation effects, iridium oxides hold a prominent place in the search for novel quantum states of matter, including, e.g., Kitaev spin liquids and topological Weyl states.

Strongly frustrated triangular spin lattice emerging from triplet dimer formation in honeycomb Li2IrO3.

Iridium oxides with a honeycomb lattice have been identified as platforms for the much anticipated Kitaev topological spin liquid: the spin-orbit entangled states of Ir(4+) in principle generate precisely the required type of anisotropic exchange. However, other magnetic couplings can drive the system away from the spin-liquid phase. With this in mind, here we disentangle the different magnetic interactions in Li2IrO3, a honeycomb iridate with two crystallographically inequivalent sets of adjacent Ir sites.

Strong magnetic frustration and anti-site disorder causing spin-glass behavior in honeycomb Li2RhO3.

With large spin-orbit coupling, the electron configuration in d-metal oxides is prone to highly anisotropic exchange interactions and exotic magnetic properties. In 5d(5) iridates, given the existing variety of crystal structures, the magnetic anisotropy can be tuned from antisymmetric to symmetric Kitaev-type, with interaction strengths that outsize the isotropic terms. By many-body electronic-structure calculations we here address the nature of the magnetic exchange and the intriguing spin-glass behavior of Li2RhO3, a 4d(5) honeycomb oxide.

Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers.

A promising route to tailoring the electronic properties of quantum materials and devices rests on the idea of orbital engineering in multilayered oxide heterostructures. Here we show that the interplay of interlayer charge imbalance and ligand distortions provides a knob for tuning the sequence of electronic levels even in intrinsically stacked oxides. We resolve in this regard the d-level structure of layered Sr2IrO4 by electron spin resonance.

Electronic structure of low-dimensional 4d(5) oxides: interplay of ligand distortions, overall lattice anisotropy, and spin-orbit interactions.

The electronic structure of the low-dimensional 4d(5) oxides Sr2RhO4 and Ca3CoRhO6 is herein investigated by embedded-cluster quantum chemistry calculations. A negative tetragonal-like t2g splitting is computed in Sr2RhO4 and a negative trigonal-like splitting is predicted for Ca3CoRhO6, in spite of having positive tetragonal distortions in the former material and cubic oxygen octahedra in the latter. Our findings bring to the foreground the role of longer-range crystalline anisotropy in generating noncubic potentials that compete with local distortions of the ligand cage, an issue not addressed in standard textbooks on crystal-field theory.

Magnetic state of pyrochlore Cd(2)Os(2)O(7) emerging from strong competition of ligand distortions and longer-range crystalline anisotropy.

By many-body quantum-chemical calculations, we investigate the role of two structural effects--local ligand distortions and the anisotropic Cd-ion coordination--on the magnetic state of Cd(2)Os(2)O(7), a spin S = 3/2 pyrochlore. We find that these effects strongly compete, rendering the magnetic interactions and ordering crucially dependent on these geometrical features. Without trigonal distortions, a large easy-plane magnetic anisotropy develops.

Ab Initio determination of Cu 3d orbital energies in layered copper oxides.

It has long been argued that the minimal model to describe the low-energy physics of the high T(c) superconducting cuprates must include copper states of other symmetries besides the canonical [see text] one, in particular the [see text] orbital. Experimental and theoretical estimates of the energy splitting of these states vary widely. With a novel ab initio quantum chemical computational scheme we determine these energies for a range of copper-oxides and -oxychlorides, determine trends with the apical Cu-ligand distances and find excellent agreement with recent Resonant Inelastic X-ray Scattering measurements, available for La(2)CuO(4), Sr(2)CuO(2)Cl(2), and CaCuO(2).