Optical gap in herringbone and pi-stacked crystals of 1]benzothieno3,2-b]benzothiophene and its brominated derivative

The optical gap of the organic semiconductor 1]benzothieno3,2-b]benzothiophene and its 2,7-dibrominated analogue is measured in solution and in the crystalline state by means of UV-vis and emission spectroscopy. Bromination leads to a change in molecular packing from herringbone to pi-stacked, resulting in a marked shift in the absorption and emission spectra which is found to be in accordance with TDDFT calculations

Ordering of hidden pseudo-dipolar moments in spin-orbital entangled 5d1 Ta chlorides

Spin-orbit coupling of as large as a half eV for electrons in 5d orbitals often gives rise to the formation of spin-orbital entangled objects, with the effective total angular momentum Jeff. Of particular interest are the Jeff = 3/2 states realized in 5d1 transition metal ions surrounded by an anion octahedron. The pure Jeff = 3/2 quartet does not have any magnetic dipolar moment (⟨M⟩ = 0) but hosts hidden pseudodipolar moments accompanied by charge quadrupoles and magnetic octupoles. Cs2TaCl6 and Rb2TaCl6 are correlated insulators with 5d1 Ta4+ ions in a regular Cl octahedron. Here we demonstrate that these Ta chlorides indeed have a substantially suppressed effective magnetic dipolar moment of ∼0.2 μB . Two phase transitions are observed at low temperatures that are not pronounced in the magnetization but accompanied with large electronic entropy of ∼Rln4. We ascribe the two transitions to the ordering of hidden multipoles

Na9Bi5Os3O24: A Diamagnetic Oxide Featuring a Pronouncedly Jahn-Teller-Compressed Octahedral Coordination of Osmium(VI)

The Jahn-Teller (JT) theorem constitutes one of the most fundamental concepts in chemistry. In transition-element chemistry, the 3d(4) and 3d(9) configurations in octahedral complexes are particularly illustrative, where a distortion in local geometry is associated with a reduction of the electronic energy. However, there has been a lasting debate about the fact that the octahedra are found to exclusively elongate. In contrast, for Na9Bi5Os3O24, the octahedron around Os6+(5d(2)) is heavily compressed, lifting the degeneracy of the t(2g) set of 5d orbitals such that in the sense of a JT compression a diamagnetic ground state results. This effect is not forced by structural constraints, the structure offers sufficient space for osmium to shift the apical oxygen atoms to a standard distance. The relevance of these findings is far reaching, since they provide new insights in the hierarchy of perturbations defining ground states of open shell electronic systems. Introductio

Coexisting Z-type charge and bond order in metallic NaRu2O4

© 2022, The Author(s).How particular bonds form in quantum materials has been a long-standing puzzle. Two key concepts dealing with charge degrees of freedom are dimerization (forming metal-metal bonds) and charge ordering. Since the 1930s, these two concepts have been frequently invoked to explain numerous exciting quantum materials, typically insulators. Here we report dimerization and charge ordering within the dimers coexisting in metallic NaRu2O4. By combining high-resolution x-ray diffraction studies and theoretical calculations, we demonstrate that this unique phenomenon occurs through a new type of bonding, which we call Z-type ordering. The low-temperature superstructure has strong dimerization in legs of zigzag ladders, with short dimers in legs connected by short zigzag bonds, forming Z-shape clusters: simultaneously, site-centered charge ordering also appears. Our results demonstrate the yet unknown flexibility of quantum materials with the intricate interplay among orbital, charge, and lattice degrees of freedom.11Nscopu

Nonmagnetic J = 0 State and Spin-Orbit Excitations in K2RuCl6K_{2}RuCl_{6}

Spin-orbit Mott insulators composed of $t^4_{2g}$ transition metal ions may host excitonic magnetism due to the condensation of spin-orbital J=1 triplons. Prior experiments suggest that the 4d antiferromagnet Ca$_2$RuO$_4$ embodies this notion, but a J=0 nonmagnetic state as a basis of the excitonic picture remains to be confirmed. We use Ru L$_3$-edge resonant inelastic x-ray scattering to reveal archetypal J multiplets with a J=0 ground state in the cubic compound K$_2$RuCl$_6$, which are well described within the LS-coupling scheme. This result highlights the critical role of unquenched orbital moments in 4d-electron compounds and calls for investigations of quantum criticality and excitonic magnetism on various crystal lattices

Nonmagnetic J = 0 State and Spin-Orbit Excitations in K2RuCl6K_{2}RuCl_{6}

Spin-orbit Mott insulators composed of $t^4_{2g}$ transition metal ions may host excitonic magnetism due to the condensation of spin-orbital J=1 triplons. Prior experiments suggest that the 4d antiferromagnet Ca$_2$RuO$_4$ embodies this notion, but a J=0 nonmagnetic state as a basis of the excitonic picture remains to be confirmed. We use Ru L$_3$-edge resonant inelastic x-ray scattering to reveal archetypal J multiplets with a J=0 ground state in the cubic compound K$_2$RuCl$_6$, which are well described within the LS-coupling scheme. This result highlights the critical role of unquenched orbital moments in 4d-electron compounds and calls for investigations of quantum criticality and excitonic magnetism on various crystal lattices

Spin waves and spin-state transitions in a ruthenate high-temperature antiferromagnet

Ruthenium compounds serve as a platform for fundamental concepts such as spin-triplet superconductivity$^1$, Kitaev spin liquids$^{2,3,4,5}$ and solid-state analogues of the Higgs mode in particle physics$^{6,7}$. However, basic questions about the electronic structure of ruthenates remain unanswered, because several key parameters (including Hund’s coupling, spin–orbit coupling and exchange interactions) are comparable in magnitude and their interplay is poorly understood, partly due to difficulties in synthesizing large single crystals for spectroscopic experiments. Here we introduce a resonant inelastic X-ray scattering (RIXS)$^{8,9}$ technique capable of probing collective modes in microcrystals of 4d electron materials. We observe spin waves and spin-state transitions in the honeycomb antiferromagnet SrRu$_2$O$_6$ (ref. $^{10}$) and use the extracted exchange interactions and measured magnon gap to explain its high Néel temperature$^{11,12,13,14,15,16}$. We expect that the RIXS method presented here will enable momentum-resolved spectroscopy of a large class of 4d transition-metal compounds