Complete field-induced spectral response of the spin-1/2 triangular-lattice antiferromagnet CsYbSe2.

Fifty years after Anderson's resonating valence-bond proposal, the spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) remains the ultimate platform to explore highly entangled quantum spin states in proximity to magnetic order. Yb-based delafossites are ideal candidate TLHAF materials, which allow experimental access to the full range of applied in-plane magnetic fields. We perform a systematic neutron scattering study of CsYbSe2, first proving the Heisenberg character of the interactions and quantifying the second-neighbor coupling. We then measure the complex evolution of the excitation spectrum, finding extensive continuum features near the 120°-ordered state, throughout the 1/3-magnetization plateau and beyond this up to saturation. We perform cylinder matrix-product-state (MPS) calculations to obtain an unbiased numerical benchmark for the TLHAF and spectacular agreement with the experimental spectra. The measured and calculated longitudinal spectral functions reflect the role of multi-magnon bound and scattering states. These results provide valuable insight into unconventional field-induced spin excitations in frustrated quantum materials.

Pressure-induced metallization in layered ReSe2.

The evolution of the crystal structure and electrical transport properties of distorted layered transition metal dichalcogenide ReSe2 was studied under high pressure up to ~90 GPa by Raman spectroscopy and electrical resistivity measurements accompanied by ab initio electronic band structure calculations. Raman spectroscopy studies indicate an isostructural phase transition due to layer sliding at ~7 GPa, to the distorted 1T-phase which remains stable up to the highest pressures employed in these experiments. From a direct band gap semiconductor at ambient pressure, ReSe2 undergoes pressure-induced metallization at pressures ~35 GPa, in agreement with the ab initio calculations. Resistivity measurements performed with different loading conditions reveal the possible emergence of superconductivity, which is most likely not an intrinsic property of ReSe2, but is rather conditioned by internal stresses upon compression.

Atomic and electronic structures evolution of the narrow band gap semiconductor Ag2Se under high pressure.

Non-trivial electronic properties of silver telluride and other chalcogenides, such as the presence of a topological insulator state, electronic topological transitions, metallization, and the possible emergence of superconductivity under pressure have attracted attention in recent years. In this work, we studied the electronic properties of silver selenide (Ag2Se). We performed direct current electrical resistivity measurements, in situ Raman spectroscopy, and synchrotron x-ray diffraction accompanied by ab initio calculations to explore pressure-induced changes to the atomic and electronic structure of Ag2Se. The temperature dependence of the electrical resistivity was measured up to 30 GPa in the 4-300 K temperature interval. Resistivity data showed an unusual increase in the thermal energy gap of phase I, which is a semiconductor under ambient conditions. Recently, a similar effect was reported for the 3D topological insulator Bi2Se3. Raman spectroscopy studies revealed lattice instability in phase I indicated by the softening of observed vibrational modes with pressure. Our hybrid functional band structure calculations predicted that phase I of Ag2Se would be a narrow band gap semiconductor, in accordance with experimental results. At a pressure of ~7.5 GPa, Ag2Se underwent a structural transition to phase II with an orthorhombic Pnma structure. The temperature dependence of the resistivity of Ag2Se phase II demonstrated its metallic character. Ag2Se phase III, which is stable above 16.5 GPa, is also metallic according to the resistivity data. No indication of the superconducting transition is found above 4 K in the studied pressure range.

Structure and electrical resistivity of mixed-valent EuNi2P2 at high pressure.

The structural properties and electrical resistivity of homogeneous mixed-valent EuNi2P2 are studied at pressures up to 45 GPa. No structural phase transition is observed in the whole pressure range and the overall pressure behavior of the structural parameters is similar to that of related compounds in the collapsed tetragonal ThCr2Si2-type structure. Electrical resistivity measured up to 31 GPa at temperatures between 4 and 300 K exhibits continuous changes from the behavior typical for a mixed-valent Eu system to that of a normal metallic system at pressures above 20 GPa, indicating a transition of the strongly mixed-valent Eu atoms with a valence ~2.5 towards a pure trivalent state. No superconductivity was observed in the whole studied pressure-temperature range.

Hybrid hard- and soft-modelling applied to analyze ultrafast processes by femtosecond transient absorption spectroscopy: study of the photochromism of salicylidene anilines.

Multivariate curve resolution-alternating least squares (MCR-ALS) of multi-experiment data analysis was successfully applied to elucidate the photodynamics of the N-(3-methylsalicylidene)-3-methylaniline by analyzing UV-vis femtosecond transient absorption spectra. The two-way data obtained present some specific difficulties linked to the nature of the transient spectra collected and to the overlapping of the photodynamics of the solvent and other contributions at short time scale (below 1 ps). Advantage was taken from the flexibility of the hybrid hard-soft multivariate curve resolution (HS-MCR) approach to consider a non-absorbing contribution in the kinetic model and to provide a functional description of the solvent in soft-modelling. The results obtained confirm the existence of an intermediate excited state in the process, which is created just after the ESIPT. It was observed that this intermediate relaxes in a few hundreds of femtosecond to the S(1) fluorescent cis-keto excited state and a decay time constant of 219 fs was found. These results confirm other femtosecond time-resolved fluorescence studies on salicylidene aniline molecules. Previous hypothesis on the formation of the trans-keto photoproduct from the S(1) fluorescent cis-keto state (time constant 14 ps) is also confirmed.

On the short carbonyl bond in bis[mu-1,2-benzisothiazol-3(2H)-one 1,1-dioxido-kappa2N:O]bis[[1,2-benzisothiazol-3(2H)-one 1,1-dioxido-kappaN]bis(imidazole)copper(II)].

The short carbonyl bond in the title compound, [Cu(2)(C(7)H(4)NO(3)S)(4)(C(3)H(4)N(2))(4)] [Liu, Huang, Li & Lin (1991). Acta Cryst. C47, 41-43], is an artifact of disorder in the isothiazol-3(2H)-one 1,1-dioxide part of the 1,2-benzisothiazol-3(2H)-one entity. In the present redetermination, all bond dimensions in the centrosymmetric dinuclear molecule are normal. The five-coordinate Cu atom shows trigonal-bipyramidal coordination. Hydrogen bonds from the imidazole donor ligand link adjacent molecules into a two-dimensional layer structure.

Experimental and theoretical vibrational study of bis(N,N-dimethylthiocarbamoylthio)acetic acid.

Harmonic vibrational analysis at HF/3-21G level is performed on the ab initio optimized molecular structure of bis(N,N-dimethylthiocarbamoylthio)acetic acid, and the outcome used in assigning the infrared spectrum of the acid. The calculated spectrum compares well with the experimental solid-state FT IR spectrum recorded at 298 and at 77 K.

Experimental and theoretical vibrational study of isatin, its 5-(NO2, F, Cl, Br, I, CH3) analogues and the isatinato anion.

Effects of 5-R substitution (R = NO2, F, Cl, Br, I, CH3) and N-deprotonation on the 4000-400 cm(-1) region of the low temperature FT IR spectrum and the molecular structure of solid isatin are investigated. Harmonic IR spectra and molecular geometries of the 5-R isatins (except for Br and I analogues) are calculated at the HF/6-31G(d, p) level and compared with the experimental solid-state data. In general, substitution has small effect on the molecular structure and the IR spectrum of isatin. The v(CO) triplet in the IR spectra of isatin and its 5-substituted analogues is resulted by vibrational splitting of the out-of-phase CO stretching, v(op)[(CO)2]. While the frequency of the v(op)[(CO)2] mode is relatively less affected by 5-substitution and mainly depends on the substituent mass, the frequency of the in-phase stretching, v(ip)[(CO)2], is strongly sensitive to both mass and electronic properties of the substituent. Substitution at C5 has relatively greater influence on the electron density and the force constant of the amide than on the ketone carbonyl group. Strong electron-donors shorten and stabilize the unusually long alpha-dicarbonyl CC bond, while electron-accepting groups tend to stretch this bond further. N-Deprotonation brings to elongation of the five membered-ring along the N-C(CO(ketone)) vector and expansion of the bonds within the alpha-dicarbonyl part. Theoretical v(CO) frequency of isatin is lowered for about 180 cm(-1) upon conversion into isatinato ion. Harmonic vibrational analysis reveals that only the highest-frequency v(CO) mode of the isolated isatinato anion can be considered good group vibration for empirical assignments in spectra of solid isatinates. Owing to the solid-state influences on the v[(CO)2] modes, no reliable spectra structure correlations could be established from the present experimental spectroscopic data.

N-Propionyl-1,2-benzisoselenazol-3(2H)-one.

The title compound, C(10)H(9)NO(2)Se, crystallizes as flat molecules linked by selenium-oxygen interactions [Se.O = 3.189 (4) A] into a linear chain along the a axis of the triclinic cell. The bond dimensions that are derived from ab initio geometry optimization calculations are similar to those determined from the diffraction measurements.

Vibrational study and spectra-structure correlations in ammonium saccharinate: comparison with the alkali saccharinates.

The FT IR spectra, at temperatures from liquid-nitrogen boiling (LNT) up to room temperature (RT), as well as the RT Raman solid-state spectra of protonated and deuterated ammonium saccharinate and of a series of alkali (Na, K, Rb, Cs) saccharinates are studied. The spectral assignments are aided with ab initio calculations on the free saccharinato anion at the HF/6-31 + + G(d,p) level. Attention is paid to the ND, CO and SO2 stretching regions. Correlation splitting is believed to be responsible for the presence of a v(CO) doublet. The averaged v(CO) frequency in (purely ionic) ammonium saccharinate is found to be the lowest in the so far studied saccharinates, along with the assumptions that the v(CO) frequency (or the corresponding averaged value) can have predictive value for the type of the metal-to-saccharinato ligand/ion bonding. The appreciably higher contribution of the dominating internal coordinate in the corresponding normal vibration in case of v(as)(SO2) than in v(s)(SO2) makes it suitable for spectra-structure correlations. Contrary to RT, even though no phase transitions were observed in the studied temperature range, some polycentered character is prescribed to the hydrogen bonds in which the ammonium ions of effective symmetry C8 participate at LNT. Certain structural predictions about the saccharinates of K, Rb and Cs are made.

Bis(N,N-dimethylthiocarbamoylthio)acetic acid.

Bis(N,N-dimethylthiocarbamoylthio)acetic acid, [(CH(3))(2)NC(=S)S](2)CHC(=O)OH or C(8)H(14)N(2)O(2)S(4), exists as a centrosymmetric hydrogen-bonded dimer [O.O 2.661 (3) A].

[The diagnosis of sialolithiasis taking into account the stage of the pathological process]. / Diagnostika sliunnokamennoi bolezni s uchetom stadii patologicheskogo protsessa.

A total of 142 patients with sialolithiasis were examined, treated, and followed up. Analysis of clinical manifestations and morphologic changes has revealed a staged pattern of this condition, depending on the sialolith localization, disease standing, and incidence of inflammation exacerbations. The authors consider that a profound study of clinical symptoms with the use of mathematical statistics methods permits a sufficiently accurate identification of the histologic stage of the process and helps define the scope of surgical intervention.

[Experimental validation of the use of the masseter muscle in treating paralysis of the mimetic muscles]. / Eksperimental'noe obosnovanie ispol'zovaniia zhevatel'noi myshtsy pri lechenii paralichei mimicheskikh myshts.

In 15 rabbits the distal end of masseter muscle was surgically transposed to perioral region. After 90, 120 and 180 days the altered muscle position and reduction of functional load did not cause its degeneration. Rather, these conditions elicited a functional reordering evidenced by reduction of muscular fibers' cross-sectional area, the number of surrounding capillaries, decrease in the succinate dehydrogenase activity and increase in connective tissue layer.