New Publications

Investigation of Microstrip High-Pass Filters Based on Multimode Resonator

Belyaev, Boris; Khodenkov, Sergey; Nazarov, Gregory; Natalia, Shepeta; Panin, Dmitry Edited by: Dolganov AY Source: 2019 URAL SYMPOSIUM ON BIOMEDICAL ENGINEERING, RADIOELECTRONICS AND INFORMATION TECHNOLOGY (USBEREIT), 383-386; 2019

NMR imaging of 3D printed biocompatible polymer scaffolds interacting with water

Morozov, Evgeny; Novikov, Mikhail; Bouznik, Vyacheslav; Yurkov, Gleb Source: RAPID PROTOTYPING JOURNAL, 25 (6):1007-1016; 10.1108/RPJ-10-2018-0271 JUL 8 2019

Active employment of additive manufacturing for scaffolds preparation requires the development of advanced methods which can accurately characterize the morphologic structure and its changes during an interaction of the scaffolds with substrate and aqueous medium. This paper aims to use the method of nuclear magnetic resonance (NMR) imaging for preclinical characterization of 3D-printed scaffolds based on novel allyl chitosan biocompatible polymer matrices.

Structural and X-ray spectroscopy studies of Pb1-xBax(NO3)(2) solid solutions

Isaenko, L. I.; Korzhneva, K. E.; Khyzhun, O. Y.; Molokeev, M. S.; Goloshumova, A. A.; Tarasova, A. Y. Source: JOURNAL OF SOLID STATE CHEMISTRY, 277 786-792; 10.1016/j.jssc.2019.07.047 SEP 2019

Pb0.75(3)Ba0.25(3)(NO3)2, Pb0.68(3)Ba0.32(3)(NO3)2, Ba0.58(3)Pb0.42(3)(NO3)2, Ba0.81(3)Pb0.19(3)(NO3)2 crystals were grown for the first time when studying the Pb(NO3)2–Ba(NO3)2–H2O system. The crystals were grown in water solution with different relation of Pb(NO3)2 and Ba(NO3)2. It was found that series of solid solutions were formed by interaction of simple Pb(NO3)2 and Ba(NO3)2 compounds with a slow increase of volume and cell parameters from pure lead nitrate to pure barium nitrate. The crystal structure of all obtained Pb1-xBax(NO3)2 crystals belong to a cubic space group Pa-3. In these structures, Pb and Ba cations have the same coordination number 12, but different ionic radii (1.49 and 1.61 Å, respectively), anionic group is an equilateral triangle with O–O–O angle of 60° and O–O bond lengths ranging from 2.1305(8) to 2.2585(7) Å. The Pb2+ ion has a lone pair of electrons that are likely to be stereochemically active in these solid solutions leading to a significant amount of local disorder which explains the spread in the lattice parameters. The Pb1-xBax(NO3)2 solid solutions were characterized by X-ray photoelectron spectroscopy (XPS) by measuring the binding energies of the core-levels of constituting atoms and the shapes of the valence band. The XPS measurements indicate that the substitution of Pb for Ba does not cause changes in the charge states of the atoms constituting the Pb1-xBax(NO3)2 crystals. Matching the XPS valence-band spectra and the X-ray emission O Kα bands on a common energy scale indicates that the principal contributions of O 2p states occur at the top of the valence band of the crystals under study with also their substantial input in the upper and central portions of the band.

Structural, thermal and optical properties of elpasolite-like (NH4)(2)KZrF7

Pogoreltsev, E., I; Mel'nikova, S., V; Molokeev, M. S.; Flerov, I. N.; Laptash, N. M. Source: JOURNAL OF SOLID STATE CHEMISTRY, 277 376-380; 10.1016/j.jssc.2019.06.013 SEP 2019

New fluoride compound (NH4)2KZrF7 with the elpasolite structure (sp. gr. Fm-3m) was synthesized by partial cationic substitution in (NH4)3ZrF7 cryolite. Due to small difference in ionic radii of K+ and NH4+, non-equivalent crystallographic positions 8c and 4b are occupied by both cations. Investigations of thermal, optical and structural properties in a wide range of temperature revealed two phase transitions Fm-3mP42/ncmP42/nmc of the first order. The results obtained are discussed in comparison with the data for the previously studied related cryolite (NH4)3ZrF7

Synthesis, structure, and properties of EuErCuS3

Ruseikina, Anna, V; Solovyov, Leonid A.; Chernyshev, Vladimir A.; Aleksandrovsky, Aleksandr S.; Andreev, Oleg, V; Krylova, Svetlana N.; Krylov, Alexander S.; Velikanov, Dmitriy A.; Molokeev, Maxim S.; Maximov, Nikolai G.; Grigoriev, Maxim, V; Garmonov, Alexander A.; Matigorov, Alexey, V Source: JOURNAL OF ALLOYS AND COMPOUNDS, 805 779-788; 10.1016/j.jallcom.2019.07.059 OCT 15 2019

The crystal structure of the first-synthesized compound EuErCuS3 was determined from X-ray powder diffraction data: orthorhombic crystal system, space group Pnma, structural type Eu2CuS3: a = 10.1005(2) Å, b = 3.91255(4)Å, c = 12.8480(2) Å; V = 507.737(14) Å3, Z = 4, and ρx = 6.266 g/cm3. The temperatures and enthalpies of reversible polymorphic transitions and incongruent melting of the compound were determined by DSC: Tα↔β = 1524 K, ΔНα↔β = 2.3 ± 0.2 kJ∙mol−1; Tβ↔γ = 1575 K, ΔНβ↔γ = 0.7 ± 0.1 kJ∙mol−1; Tγ↔δ = 1602 K; ΔНγ↔δ = 1.3 ± 0.1 kJ∙mol−1 and Tcr = 1735 ± 10 K, ΔНcr = −3.5 ± 0.3 kJ∙mol−1. IR spectra were recorded in the range from 50 to 400 cm−1. The compound was found to be IR-transparent in the range 4000–400 cm−1. The compound was characterized by Raman spectroscopy. The observed spectra featured both Raman lines and luminescence. Ab initio calculations of the EuErCuS3 crystal structure and phonon spectrum were performed, the frequencies and types of fundamental modes were determined, and the involvement of constituent ions in the IR and Raman modes was assessed from an analysis of the ab initio displacement vectors. The vibrational spectra were interpreted. EuErCuS3 manifests a ferrimagnetic transition at 4.8 K. Its microhardness is 2850 MPa. The obtained data can serve as the basis for predicting the properties of EuLnCuS3 compounds. Valence states for Eu (2+) and Er (3+) are proved both by the XRD and optical methods. Optical band gap was found to be 1.934 eV from diffuse reflectance spectrum.

Specific features of Nd3+ Kramers doublets' splitting in an antiferromagnetic crystal NdFe3(BO3)(4) in an external magnetic field

Gnatchenko, S. L.; Kachur, I. S.; Kurnosov, V. S.; Piryatinskaya, V. G.; Malakhovskii, V; Gudim, I. A. Source: LOW TEMPERATURE PHYSICS, 45 (8):928-933; 10.1063/1.5116545 AUG 2019

The optical absorption spectra of an easy-plane NdFe3(BO3)4 antiferromagnet are measured in the region of the 4I9/2 → 2H11/2 transition of the of Nd3+ ion. The study is performed in the 2–35 К temperature range, in external magnetic fields of up to 65 kOe directed both along the С3 axis and the basal plane of the crystal. The splitting values of the Nd3+ excited states in the exchange field of the Fe3+ subsystem and the g-factors of the 2H11/2 multiplet states are determined. The nontrivial dependences of the splitting of some Nd3+ states in a magnetic field indicate that these states have anisotropic Fe–Nd exchange interaction.

Magnetoelectric Effect in a Paramagnetic Region in Gd0.15Mn0.85Se

Aplesnin, S. S.; Kretinin, V. V.; Begisheva, O. B. Source: PHYSICS OF THE SOLID STATE, 61 (8):1379-1382; 10.1134/S1063783419080067 AUG 2019

The electric polarization in a zero magnetic field and in a magnetic field of 12 kOe is measured in a GdxMn1 – xSe solid solution in the percolation concentration region in the temperature range 80–380 K. For composition x = 0.15, the polarization hysteresis and the dependence of the remanent polarization on magnetic field and temperature are determined. The hysteresis is explained in the model of migration polarization and the magnetoelectric effect is explained in the Maxwell–Wagner model.

Role of Halogen Atoms on High-Efficiency Mn2+ Emission in Two-Dimensional Hybrid Perovskites

Zhou, Guojun; Jia, Xiaofang; Guo, Shaoqiang; Molokeev, Maxim; Zhang, Junying; Xia, Zhiguo Source: JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10 (16):4706-4712; 10.1021/acs.jpclett.9b01996 AUG 15 2019

Doped halide pervoskites as highly efficient light emitters have recently fascinated the research community, while the influence of halogen atoms X (X = Cl, Br, I) on the hybrid energy levels and photoluminescence properties remains a challenge. Here, the role of X compositions in the two-dimensional hybrid perovskite BA2PbX4 (BA = C4H9NH3) on the doped Mn2+ emission is identified, wherein Mn2+ reveals a strong luminescence dependence on the nature of the halogen, and optimum Mn2+ emission with a record quantum yield of 60.1% has been achieved in BA2PbBr4. Density functional theory calculations show that BA2PbBr4 holds low Br vacancy concentration and unique coupled states of the Mn-3d level and Pb-6p level at the conduction band minimum, leading to efficient energy transfer from the host to Mn2+. Our work sheds new light on the methods to realize strong exciton–dopant exchange coupling for achieving high-efficiency dopant luminescence.

The role of strong electron correlations in determination of band structure and charge distribution of transition metal dihalide monolayers

Kovaleva, E. A.; Melchakova, Iuliia; Mikhaleva, N. S.; Tomilin, F. N.; Ovchinnikov, G.; Baek, Woohyeon; Pomogaev, V. A.; Avramov, P.; Kuzubov, A. A. Source: JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 134 324-332; 10.1016/j.jpcs.2019.05.036 NOV 2019

Electronic structure and magnetic properties of the family of first-row transition metal dihalides (TMHal2, TM = V, Cr, Mn, Fe, Co, Ni; H = Br, I) monolayers were studied by means of density functional theory. Strong electron correlations were taken into account by implementing Hubbard U correction in a simplified scheme proposed by Dudarev et al. (Ueff). Ueff correction essentially affects electronic structure of TMHal2 widening the band gap and witnessing their highly spin-polarized nature. Two different ligand orientations namely, H and T configurations of monolayers were considered. Unlike others, FeHal2 monolayers tend to form H structure when Ueff correction is included.

Multi-channel bound states in the continuum in coaxial cylindrical waveguide

Pilipchuk, A. S.; Pilipchuk, A. A.; Sadreev, A. F. Source: PHYSICA SCRIPTA, 94 (11):10.1088/1402-4896/ab1e9b NOV 2019

Bound states in the continuum (BICs) or embedded trapped modes are widely studied in different physical systems. The studies are restricted to a single open scattering channel. In the present paper we consider BICs embedded into several continua in a cylindrical resonator opened by two coaxially attached cylindrical waveguides with different radii. We demonstrate that engineering the BICs requires a degeneracy of three eigenmodeds of the closed resonator. That is achieved by variation of both the length and the radius of the resonator.

Stability of the Coexistence Phase of Chiral Superconductivity and Noncollinear Spin Ordering with a Nontrivial Topology and Strong Electron Correlations

Val'kov, V. V.; Zlotnikov, A. O. Source: JETP LETTERS, 109 (11):736-743; 10.1134/S0021364019110158 JUN 2019

It has been shown that quantum charge and spin fluctuations in a strongly correlated 2D system with a triangular lattice, significantly renormalizing the magnetic order parameter, do not destroy the coexistence phase of chiral d + id superconductivity and 120° spin ordering. The region of realization of nontrivial topology determined by the topological index Ñ3 holds. It has been shown that edge states for the topologically non-trivial phase include a Majorana mode. The spatial structure of this mode has been determined. It has been found that spin and charge fluctuations shift the critical electron densities at which quantum topological transitions occur. It has been shown that an increase in the intersite Coulomb repulsion reduces the number of such transitions.

Structure of Barbituratobis(2,2 '-Dipyridyl)copper(II) Heptahydrate

Golovnev, N. N.; Molokeev, M. S.; Sterkhova, I. V.; Lesnikov, M. K. Source: RUSSIAN JOURNAL OF COORDINATION CHEMISTRY, 45 (8):569-572; 10.1134/S1070328419080037 AUG 2019

The structure of the complex [Cu(Bipy)2(BA)] ∙ 7H2O (I), where Bipy is 2,2'-dipyridyl, and BA2– is the barbituric acid anion (H2BA), is determined (CIF file CCDC no. 1887338). The thermal decomposition and IR spectrum of complex I are studied. The crystals are orthorhombic: a = 26.118(3), b = 27.685(3), c = 15.683(2) Å, V = 11 370(2) Å3, space group Fdd2, Z = 16. The discrete structure of the polar crystal consists of neutral [Cu(Bipy)2(BA)] particles and molecules of crystallisation water . The Cu2+ ion is bound to the N atoms of two bidentate Bipy molecules and the N atom of the BA2− ion at the vertices of the trigonal bipyramid CuN5. Compound I is the first example of the metal complex only with the N-coordinated anions of barbituric acid (BA2−, НBA). The structure is stabilized by hydrogen bonds O−H∙∙∙O and N−H∙∙∙O to form a three-dimensional network with the π–π interaction between the Bipy molecules. The compound begins to lose water at ~50°С and is completely dehydrated above 200°С.

Optically Modulated Ultra-Broad-Band Warm White Emission in Mn2+-Doped (C6H18N2O2)PbBr4 Hybrid Metal Halide Phosphor

Zhou, Guojun; Jiang, Xingxing; Molokeev, Maxim; Lin, Zheshuai; Zhao, Jing; Wang, Jing; Xia, Zhiguo Source: CHEMISTRY OF MATERIALS, 31 (15):5788-5795; 10.1021/acs.chemmater.9b01864 AUG 13 2019

Finding new low-dimensional metal halides with broad-band emission is attracting interest in single-component phosphor for white light-emitting diodes (WLEDs). The full-spectrum white light still remains a challenge as found in the two-dimensional hybrid material (C6H18N2O2)PbBr4 exhibiting the intrinsic free exciton (FE) and broad-band self-trap exciton (STE) emission upon 365 nm ultraviolet excitation, and a combined strategy has been proposed through doping the Mn2+ ions enabling a superposition of multiple emission centers toward the ultra-broad-band warm white light. The occupation of Mn2+ in (C6H18N2O2)PbBr4 has been discussed, and optical investigations verify that the warm white-light emission of Mn2+-doped (C6H18N2O2)PbBr4 originates from the coupling effects of the FE, STEs, and the 4T16A1 transition of the doped Mn2+. When the concentration of Mn2+ is 5%, the emission spectrum of the phosphor covers all visible-light areas with a full width at half maximum (FWHM) of about 230 nm. The high Ra (84.9) and warm light CCT (3577 K) values of the as-fabricated WLED lamp demonstrate that (C6H18N2O2)Pb1–xMnxBr4 can be promising as single-component white-light phosphor in solid-state lighting. Our work could provide a new understanding and perspective about hybrid metal halides for designing superior phosphor toward single-component white emission.

Strong Spin-Charge Coupling and Its Manifestation in the Quasiparticle Structure, Cooper Instability, and Electromagnetic Properties of Cuprates

Val'kov, V. V.; Dzembisashvili, D. M.; Korovushkin, M. M.; Komarov, K. K.; Barabanov, A. F. Source: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 128 (6):885-898; 10.1134/S1063776119050078 JUN 2019

The Fermi excitation spectrum, the problem of Cooper instability, and the Londons magnetic field penetration depth in cuprate superconductors are considered using the unified conception based on accounting for the strong coupling between the spin of copper ions and holes at oxygen ions. This coupling leads to strong renormalization of the primary spectrum of oxygen holes with the formation of spin-polaron quasiparticles. Analysis of Cooper instability performed using the spin-polaron concept for different channels has shown that only the superconducting d-wave pairing occurs in the ensemble of spin-polaron quasiparticles, and there are no solutions corresponding to the s-wave pairing. It has been demonstrated that the superconducting d-wave pairing is not suppressed by the Coulomb repulsion of holes located at neighboring oxygen ions. This effect is due to peculiarities in the crystallographic structure of the CuO2 plane and the aforementioned strong spin–fermion coupling. As a result, such interaction of holes is omitted in the kernel of the integral equation for the superconducting order parameter with the d-wave symmetry. It has been shown the Hubbard repulsion of holes and their interaction for the second coordination sphere of the oxygen sublattice for actual intensities of the interaction do not suppress the d-wave type of superconductivity. For the spin-polaron ensemble, we have analyzed the dependence of the Londons magnetic field penetration depth on the temperature and hole concentration. It has been established that the peculiarities of this dependence are closely related to specific features of the spin-polaron spectrum.

Polyhedron Transformation toward Stable Narrow-Band Green Phosphors for Wide-Color-Gamut Liquid Crystal Display

Liao, Hongxu; Zhao, Ming; Zhou, Yayun; Molokeev, Maxim S.; Liu, Quanlin; Zhang, Qinyuan; Xia, Zhiguo Source: ADVANCED FUNCTIONAL MATERIALS, 29 (30):10.1002/adfm.201901988 JUL 2019

A robust and stable narrow‐band green emitter is recognized as a key enabler for wide‐color‐gamut liquid crystal display (LCD) backlights. Herein, an emerging rare earth silicate phosphor, RbNa(Li3SiO4)2:Eu2+ (RN:Eu2+) with exceptional optical properties and excellent thermal stability, is reported. The resulting RN:Eu2+ phosphor presents a narrow green emission band centered at 523 nm with a full width at half maximum of 41 nm and excellent thermal stability (102%@425 K of the integrated emission intensity at 300 K). RN:Eu2+ also shows a high quantum efficiency, an improved chemical stability, and a reduced Stokes shift owing to the modified local environment, in which [NaO8] cubes replace [LiO4] squares in RbLi(Li3SiO4)2:Eu2+ via polyhedron transformation. White light‐emitting diode (wLED) devices with a wide color gamut (113% National Television System Committee (NTSC)) and high luminous efficacy (111.08 lm W−1) are obtained by combining RN:Eu2+ as the green emitter, K2SiF6:Mn4+ as the red emitter, and blue‐emitting InGaN chips. Using these wLEDs as backlights, a prototype 20.5 in. LCD screen is fabricated, demonstrating the bright future of stable RN:Eu2+ for wide‐color‐gamut LCD backlight application.

Scattering of Electromagnetic Waves on a Subwave Lattice of Square Strip Conductors

Belyaev, B. A.; Tyurnev, V; Volkov, N. V. Source: JOURNAL OF COMMUNICATIONS TECHNOLOGY AND ELECTRONICS, 64 (7):664-674; 10.1134/S1064226919070039 JUL 2019

Simple formulas are obtained for calculating the scattering matrix of a plane electromagnetic wave incident normally on an infinite 2D lattice formed by square strip conductors and located at the interface of two dielectric media. For the first time, the vortex behavior of the electric field of the lattice was taken into account, which made it possible to repeatedly reduce the computation error at high frequencies. This is confirmed by the close agreement of the amplitude-frequency responses of the structure calculated by the formulas with the characteristics obtained by the numerical electrodynamic analysis of the 3D model when the lattice period is less than half the wavelength.

Automated Measuring Unit for Analysis of Thin Magnetic Film Ferroresonance Spectrum

Burmitskikh, Anton V.; Boev, Nikita M.; Izotov, Andrey V.; Andyuseva, Valentina G. Edited by: Stukach O Source: 2019 INTERNATIONAL SIBERIAN CONFERENCE ON CONTROL AND COMMUNICATIONS (SIBCON), 2019 Book Series: IEEE International Siberian Conference on Control and Communications

Compact Non-Linear Power Amplifier for Wideband Underwater and Underground Near-Field Magnetic Communication Systems

Belyaev, Boris A.; Babitskii, Alexander N.; Boev, Nikita M.; Izotov, Andrey V.; Sushkov, Artem A.; Korolev, Eugene V.; Burmitskikh, Anton V. 2019 INTERNATIONAL SIBERIAN CONFERENCE ON CONTROL AND COMMUNICATIONS (SIBCON), 2019. Book Series: IEEE International Siberian Conference on Control and Communications

Dual wavelength Talbot self-imaging using facet patterned nonlinear crystals

Vyunishev, A. M.; Myslivets, S. A.; Fokin, V. A.; Volochaev, M. N.; Smolyarova, T. E.; Radionov, N., V; Zaitsev, A., I; Arkhipkin, V. G.; Chirkin, A. S. Source: OPTICS LETTERS, 44 (15):3761-3764; 10.1364/OL.44.003761 AUG 1 2019

A method for functional patterning of facets of a nonlinear crystal using focused ion beam milling has been developed. The near-field diffraction on periodic gratings has been experimentally and theoretically studied. The periodicity of the structure enables Talbot self-imaging at the fundamental and second-harmonic frequencies simultaneously. Spatial interference patterns for both harmonic frequencies are individual ones, which can enable the higher-accuracy optical testing, coupling the radiation at both frequencies, and wavelength-division demultiplexing. The impact of the aperture effect on a Talbot carpet is discussed.

Broadband Tamm plasmon polariton

Vyunishev, Andrey M.; Bikbaev, Rashid G.; Svyakhovskiy, Sergey E.; Timofeev, Ivan, V; Pankin, Pavel S.; Evlashin, Stanislav A.; Vetrov, Stepan Ya; Myslivets, Sergey A.; Arkhipkin, Vasily G. Source: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 36 (8):2299-2305; 10.1364/JOSAB.36.002299 AUG 1 2019

A broadband Tamm plasmon polariton localized at the interface between the Bragg mirror and a thin metallic layer has been theoretically and experimentally investigated. The possibility of a localized state formation has been demonstrated and energy coefficients at the Tamm plasmon polariton wavelength have been predicted in the framework of the coupled mode theory. The metallic layer material and thickness corresponding to the maximum coupling between the incident radiation and the Tamm plasmon polariton has been determined. Experimental reflectance and transmittance spectra of the structure consisting of the Bragg mirror and chromium layers of different thicknesses have been measured. The analysis of the energy spectra shows the existence of the wavelength range with the near-unity absorption coefficient inside the Bragg mirror bandgap. The use of chromium as a metal results in the broadband Tamm plasmon polariton excitation. It is demonstrated that the experimental data is in a good agreement with the calculation.

Magnetoresistance Hysteresis Evolution in the Granular Y-Ba-Cu-O High-Temperature Superconductor in a Wide Temperature Range

Semenov, S. V.; Balaev, D. A. Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (8):2409-2419; 10.1007/s10948-019-5043-2 AUG 2019

The temperature evolution of the magnetoresistance hysteresis in the granular YBa2Cu3O7-δ high-temperature (TC ≈ 92 K) superconductor has been investigated. The measurements have been performed in the high-temperature region (78–90 K) and at the liquid helium temperature (4.2 K). The results obtained have been analyzed using the developed model of the behavior of transport properties of a granular high-temperature superconductor in an external magnetic field. Within the discussed model, the dissipation of the grain boundary subsystem is determined by the intergrain spacing-averaged effective field Beff, which is a superposition of external field H and the field induced by the magnetic moments of superconducting grains. Such a consideration yields the expression Beff(H) = H − 4πM(H) α for the effective field in the intergrain medium, where M(H) is the experimental hysteretic dependence of magnetization and α is the parameter of magnetic flux crowding in the intergrain medium. Here, the magnetoresistance is assumed to be proportional to the absolute value of the effective field: R(H) ~ |Beff(H)|. Analysis of the experimental R(H) and M(H) dependences obtained under the same conditions for the investigated high-temperature superconductor sample showed that in the high-temperature region this parameter is α ≈ 25. At the low temperature (4.2 K), we may state that the degree of flux crowding increases and the estimated α value is ~ 50. The estimates made are indicative of the strong effect of flux compression in the intergrain medium on the magnetotransport properties of the investigated granular high-temperature superconductor system. Possible reasons for a discrepancy between the developed model concepts and experimentally observed low-temperature R(H) hysteresis are analyzed.

Bound states in the continuum and Fano resonances in the Dirac cone spectrum

Bulgakov, Evgeny N.; Maksimov, Dmitrii N. Source: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 36 (8):2221-2225; 10.1364/JOSAB.36.002221 AUG 1 2019

We consider light scattering by two-dimensional arrays of high-index dielectric spheres arranged into a triangular lattice. It is demonstrated that in the case of a triple degeneracy of resonant leaky modes in the gamma point, the scattering spectra exhibit a complicated picture of Fano resonances with extremely narrow linewidth. The Fano features are explained through coupled-mode theory for a Dirac cone spectrum as a signature of optical bound states in the continuum (BIC). It is found that the standing wave in-gamma BIC induces a ring of off-gamma BICs due to different scaling laws for real and imaginary parts of the resonant eigenfrequencies in the Dirac cone spectrum. A quantitative theory of the spectra is proposed

IR-range photoinduced diode effect in the manganese-substituted bismuth ferrite films

Aplesnin, S. S.; Kretinin, V. V.; Masyugin, A. N.; Romanova, O. B.; Sitnikov, M. N.; Begisheva, O. B.; Galyas, A., I; Demidenko, O. F.; Yanushkevich, K., I Source: SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 34 (9):10.1088/1361-6641/ab3160 SEP 2019

The photoinduced diode effect has been found in BiMn X Fe1−X O3 (0 < Х < 0.15) films in the near-infrared and violet spectral ranges in a wide temperature interval. The dependences of the diode effect on temperature, wavelength, and illumination power have been established. The mechanism of the ferroelectric diode has been determined using its IV characteristics at different illumination powers, optical spectra, far-infrared absorption spectra, and electric polarization hysteresis. The interplay between the photodiode effect and conductivity mechanism has been elucidated. The model of strong Coulomb potential fluctuations and quantum well asymmetry caused by the electric polarization in the film and difference between the times of carrier thermalization and recombination of electrons and holes is proposed.

Phase transitions in bismuth pyrostannate upon substitution of tin by iron ions

Udod, L., V; Aplesnin, S. S.; Sitnikov, M. N.; Romanova, O. B.; Molokeev, M. N. Source: JOURNAL OF ALLOYS AND COMPOUNDS, 804 281-287; 10.1016/j.jallcom.2019.07.020 OCT 5 2019

The Bi2(Sn1-хFeх)2O7 (х = 0, 0.1, 0.2) compounds have been synthesized by the solid-state reaction technique. The structure of the synthesized compounds has been investigated in the temperature range of 80–500 K using the thermal expansion and ultrasound damping coefficients and IR spectroscopy. The shift -type structural transitions for the composition with х = 0.2 in the low-temperature region has been established. The effect of iron ions on the phase boundaries of the polymorphic transitions in the Bi2Sn2O7 compound has been observed. Softening of the phonon modes near the phase transitions at different iron concentrations has been found.

Soft modes condensation in Raman spectra of (Pb-La)(Zr-Sn-Ti)O-3 ceramics

Vtyurin, Alexander N.; Krylov, Alexander S.; Krylova, Svetlana N.; Oreshonkov, Alexander S.; Wei, Xiaoyong; Feng, Yujun; Xu, Ran; Zhao, Tian Source: JOURNAL OF ADVANCED DIELECTRICS, 9 (3):10.1142/S2010135X19500243 JUN 2019

Low frequency Raman spectra of (Pb0.97La0.02)(Zr0.864Sn0.04Ti0.096)O3 ceramic samples have been studied near cubic to antiferroelectric phase transition at about 200C. A set of low frequency soft modes were observed restoring below the transition point, in addition to the known one above 100cm1. These modes show strong damping anomalies at the transition point that supposes considerable intermode interactions via dampings.

Magnetic Properties of Soft Magnetic Alloys 5BDSR and 82K3HSR

Svetlichnyi, V. A.; Balashov, V. B.; Lapin, I. N.; Sokolov, A. E.; Cherepanov, V. N. Source: RUSSIAN PHYSICS JOURNAL, 62 (3):411-415; 10.1007/s11182-019-01728-6 JUL 2019

The paper explores the size and morphology of microparticles of soft magnetic alloys 5BDSR and 82K3HSR and nanoparticles first obtained from these alloys using pulsed laser ablation in gas. The magnetic properties of particles are studied depending on their size, composition and production method.

Tunnel Conductivity and Tunnel Magnetoresistance of the Fe-SiO Films: Interplay of the Magnetotransport and Magnetic Properties

Balaev, D. A.; Balaev, A. D. Source: PHYSICS OF THE SOLID STATE, 61 (7):1203-1210; 10.1134/S1063783419070047 JUL 2019

The electrical properties of a system of nanogranular amorphous Fe–SiO films with a SiO concentration between 0 and 92 vol % have been investigated. The samples with a low SiO content are characterized by the metal-type conductivity. With an increase in the dielectric content x in the films, the concentration transition from the metal to tunneling conductivity occurs at x ≈ 0.6. At the same concentration, the ferromagnet–superparamagnet transition is observed, which was previously investigated by the magnetic method. The temperature dependences of the electrical resistivity ρ(T) for the compositions corresponding to the dielectric region obey the law ρ(T) ~ exp(2(C/kT)1/2), which is typical of the tunneling conductivity. The estimation of the metal grain sizes from the tunneling activation energy C has shown good agreement with the sizes obtained previously by analyzing the magnetic properties. In the dielectric region of the compositions, the giant magnetoresistive effect attaining 25% at low temperatures has been obtained.

Orientational structures in cholesteric droplets with homeotropic surface anchoring

Krakhalev, Mikhail N.; Rudyak, Vladimir Yu.; Prishchepa, Oxana O.; Gardymova, Anna P.; Emelyanenko, Alexander V.; Liu, Jui-Hsiang; Zyryanov, Victor Ya. Source: SOFT MATTER, 15 (28):5554-5561; 10.1039/c9sm00384c JUL 28 2019

The dependency of orientational structures in cholesteric droplets with homeotropic surface anchoring on the helicity parameter has been studied by experiment and simulations. We have observed a sequence of structures, in which the director configurations and topological defects were identified by comparison of polarized microscopy pictures with simulated textures. A toron-like and low-symmetry intermediate layer-like structures have been revealed and studied in detail. The ranges of stability of the observed structures have been summarized in a general diagram and explained by the helicity parameter dependence of the free energy terms.

Structure and electrophysical properties of thin-film SnO2-In2O3 heterostructures

Zhilova, O. V.; Pankov, S. Yu.; Sitnikov, A. V.; Kalinin, Yu. E.; Volochaev, M. N.; Makagonov, V. A. Source: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 30 (13):11859-11867; 10.1007/s10854-019-01503-w JUL 2019

The structure and electrical properties of In2O3 and SnO2 oxide semiconductors and heterostructures based on them has been experimentally investigated. The films were prepared by the method of layer-by-layer deposition using the ion-beam sputtering. The transition from the two-phase film of amorphous SnO2 and In2O3 islands, formed during the layer-by-layer deposition, to a multilayer structure consisting of the amorphous SnO2 and In2O3 continuous layers occurs with an increase in the bilayer thickness. The electrophysical properties of the (SnO2/In2O3)69 heterostructures are determined by the transition from the random distribution of SnO2 and In2O3 amorphous phases to a multilayer structure and the temperature range of measurement. For all studied systems, a consistent change in the prevailing mechanism of conductivity is observed at temperatures from 77 to 300 K. In (SnO2/In2O3)69 thin films with a bilayer thickness hbl < 2.5 nm, change of the prevailing conduction mechanism takes place according to the next sequence: variable range hopping conduction over localized states near the Fermi level, hopping conduction over the nearest neighbors and hopping transfer of carriers excited into localized states near the band edges at temperatures close to room temperature.

Effect of CuO2 Lattice Strain on the Electronic Structure and Properties of High-T-c Cuprate Family

Makarov, I. A.; Gavrichkov, V. A.; Shneyder, E. I.; Nekrasov, I. A.; Slobodchikov, A. A.; Ovchinnikov, S. G.; Bianconi, A. Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (7):1927-1935; 10.1007/s10948-018-4936-9 JUL 2019

Doping and strain dependences of the electronic structure of the CuO6-octahedra layer within LDA+GTB method in the frameworks of six-band p-d model are calculated. Band structure and Fermi surface of the quasiparticle excitations in the effective Hubbard model are characterized by inhomogeneous distribution of the k-dependent spectral weight. Doping results in reconstruction of the band structure, redistribution of the spectral weight over dispersion surface, and reconstruction of Fermi surface from small hole pockets in the underdoped region to large hole contour in the overdoped region through two quantum phase transitions (QPT). Strain increasing leads to displacement of the valence and conductivity bands, bandwidths decreasing, and shift of the concentrations corresponding to QPTs. Strain dependences of the antiferromagnetic exchange coupling and DOS at the Fermi level determining superconducting temperature Tc are obtained. Effective exchange coupling in the equation for Tc demonstrates monotonic strain dependence.

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