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Using wide-band (0.5-6.5 eV) spectroscopic ellipsometry we study ultrathin [Bi(0.6-2.5 nm)-FeNi(0.8,1.2 nm)]N multilayer films grown by rf sputtering deposition, where the FeNi layer has a nanoisland structure and its morphology and magnetic properties change with decreasing the nominal layer thickness. From the multilayer model simulations of the ellipsometric angles, Psi(omega) and Delta(omega), the complex (pseudo)dielectric function spectra of the Bi layer were extracted. The obtained results demonstrate that the Bi layer can possess the surface metallic conductivity, which is strongly affected by the morphology and magnetic properties of the nanoisland FeNi layer in the GMR-type Bi-FeNi multilayer structures., 6 pages, 4 figures

The article presents the analysis and evaluation of a new innovative textbook “Information technology support of legal activity (LegalTech): textbook / under the general editorship of A. V. Minbaleev / of the Kutafin Moscow State Law University (MSAL) — Moscow: Prospect, 2022. 368 p.”, prepared by the staff of the Department of information law and digital technologies of the Kutafin Moscow State Law University (MSAL). The textbook reveals the essence and main directions of the development of LegalTech. The purpose is to identify the advantages and disadvantages of the reviewed work. It is noted that the textbook aims to develop digital innovations in professional legal activity and contribute to the formation of new knowledge in the field of LegalTech. It is concluded that the innovative nature of the textbook is also reflected in its structure, reflecting the synergy of legal activities and information technologies that have become an integral part of legal procedures in various industries.

Using dc transport and wide-band spectroscopic ellipsometry techniques, we study localization effects in the disordered metallic Ta interlayer of different thickness in the multilayer films (MLFs) (Ta - FeNi)_N grown by rf sputtering deposition. In the grown MLFs, the FeNi layer was 0.52 nm thick, while the Ta layer thickness varied between 1.2 and 4.6 nm. The Ta layer dielectric function was extracted from the Drude-Lorentz simulation. The dc transport study of the MLFs implies non-metallic (dr/dT, 11 pages, 4 figures

The article studies the problems of the legality of the use of sanctional mechanisms in the Internet. Currently, the regulation of digital platforms is the main focus of legal policy in many developing countries. Thus, there are three main directions for strengthening the legal regulation of Internet platforms: firstly, the change in the regulation of online platforms and the formation of uniform rules on the territory of the European Union, which contributes to increasing the competitive ability in this area; secondly, the strengthening of control over contents that incites hostility and hatred on the Internet, and thirdly, the development of a single bill in the field of confidential data. It is concluded that the application of sanctions is the most important regulator of information relations in the Internet. The use of higher fines effectively affects the behavior of participants in legal relations. However, the size of the fine should be supported by enforcement processes—for example, representative localization requirements.

Even the most conservative teachers and educational institutions were forced to accept the harsh reality and begin distance learning using modern technologies. Training takes place not only in electronic form, but also in real time (online). The Russian legislation, despite the fact that it has long provided for the use of remote technologies and e-learning, does not provide a clear understanding of the difference in these concepts. The article analyzes the concepts of distance, electronic and online education, proposes definitions and their relationship. Distance education (education) should be understood as the way of obtaining education, in which there are no training sessions conducted by direct interaction of the teacher with the student in the audience. Electronic education (learning) refers to the method of obtaining education through electronic means: computer technology, networks, software, etc. Online education (learning) is a way of obtaining education by interacting a teacher with a student in real time using electronic means. The main problem of distance learning in all its manifestations remains the irrelevance of the student. Teachers should be able to record an online exam, seminar or any other stage of training without obtaining the consent of the student, so that in case of controversial situations they can again evaluate the answer and check for signs of non-independent response. Distance education is a promising area in subsequent years, and the spread of coronavirus infection prompted it to develop rapidly. For e-education to become truly high-quality, adequate state support is needed, including at the legislative level.

Using atomic-force microscopy (AFM) and wide-band (0.02&ndash, 8.5 eV) spectroscopic ellipsometry techniques, we investigated the morphology and optical properties of Cd3As2 films grown by non-reactive RF magnetron sputtering on two types of oriented crystalline substrates (100)p-Si and (001) &alpha, Al2O3. The AFM study revealed the grainy morphology of the films due to island incorporation during the film growth. The complex dielectric function spectra of the annealed Cd3As2/Al2O3 films manifest pronounced interband optical transitions at 1.2 and 3.0 eV, in excellent agreement with the theoretical calculations for the body centered tetragonal Cd3As2 crystal structure. We discovered that due to electronic excitations to the Cd(s) conical bands, the low-energy absorption edge of the annealed Cd3As2 films reveals a linear dependence. We found that for the annealed Cd3As2 films, the Cd(s) conical node may be shifted in energy by about 0.08&ndash, 0.18 eV above the heavy-flat As(p) valence band, determining the optical gap value. The as-grown Cd3As2 films exhibit the pronounced changes of the electronic band structure due to the doping effect associated with Cd non-stoichiometry, where fine-tuning of the Cd concentration may result in the gapless electronic band structure of Dirac semimetals.

The actual task of analyzing and predicting the dynamics of the main crime indicators in the field of computer information is investigated. The registered values of the key parameters from the official statistics of the Ministry of the Interior are considered as indicators. To solve the problem, mathematical software is proposed based on the principles of system dynamics. The proposed complexes of models include causal matrices reflecting direct and inverse relationships between the variables in question, and systems of nonlinear differential equations. Causal matrices are based on the study of the correlation of the values of the variables in question, given from statistics. Systems of differential equations are built on the basis of cause-effect matrices and principles of system dynamics. The solution of these systems of differential equations by approximate methods makes it possible to analyze trends and make predictions of the values of the variables in question at different time intervals with fairly high accuracy. Experiments with the developed models will allow us to quantify the effect of various factors on the growth or decrease in crime in the field of computer information. The use of the developed software is shown in an example that compares the effect of the number of sentences and new legislation on reducing the number of computer crimes. The results are intended to support decision-making on combating crime in the field of computer information.

Thin Ni-Fe films were produced via electrodeposition onto silicon substrate using direct current and pulse (with different pulse durations) regimes. The correlation between technological regimes and chemical composition and microstructure for Ni-Fe nanogranular films was discussed. Analysis of the microstructure evolution revealed the changing mechanism of the films growth from the Volmer-Weber (describes island film growth) to the Stranski-Krastanov (layer by layer at the growth beginning) with the shortening of the pulse duration less than 10 μs. This anomalous behavior was explained by an increase of the binding energy between the initial atoms and the substrate surface. The results showed that using electrodeposition regimes, which ensure growth with the average crystal size less than the critical value (10 nm), provides less roughness, defectiveness and greater film uniformity in thickness, and, therefore, stable properties.

Thin Ni–Fe films were produced via electrodeposition onto silicon substrates using direct current and pulse current (with different pulse durations) regimes. The correlation between the technological regimes, chemical composition and microstructure of Ni–Fe nanogranular films was investigated. Analysis of the microstructure evolution revealed that the mechanism of film growth changes from Volmer–Weber (island film growth) to Stranski–Krastanov (layer by layer growth) with the shortening of the pulse duration below 10 μs. This anomalous behavior was explained by the increase of the binding energy between the initial film atoms and the substrate surface. The results showed that using electrodeposition regimes, which ensure growth with an average crystal size less than the critical value of 10 nm, provides less roughness and defectiveness and better film uniformity in thickness.

The article provides descriptions of the new genus and species of parasitic copepods: Chauvanium chauvani gen. et sp. nov. from Alepes melanoptera Swainson, 1839 (Perciformes: Carandidae), Sagum vietnamiensis from an unidentified fish species, and Hatschekia hanguyenvani from Lutjanus (Perciformes: Lutjanidae).

A parallel structure mechanism with six degrees of freedom and motors placed on the base outside the working area is presented. Structure of such mechanism and its operating principle are considered in detail. Model of the mechanism output link dynamics subject to elastic forces, appearing in its links and acting on the output link, is given and the equations of motion are obtained. Example of motion analysis according to these equations is shown. The obtained results are tested successfully at an experimental setup.

In magnetic compounds with Jahn–Teller (JT) ions (such as Mn3+ or Cu2+), the ordering of the electron or hole orbitals is associated with cooperative lattice distortions. There the role of JT effect, although widely recognized, is still elusive in the ground state properties. Here we discovered that, in these materials, there exist excitations whose energy spectrum is described in terms of the total angular momentum eigenstates and is quantized as in quantum rotors found in JT centers. We observed features originating from these excitations in the optical spectra of a model compound LaMnO3 using ellipsometry technique. They appear clearly as narrow sidebands accompanying the electron transition between the JT split orbitals at neighboring Mn3+ ions, displaying anomalous temperature behavior around the Neel temperature T N ≈ 140 K. We present these results together with new experimental data on photoluminescence found in LaMnO3, which lend additional support to the ellipsometry implying the electronic-vibrational origin of the quantum rotor orbital excitations. We note that the discovered orbital excitations of quantum rotors may play an important role in many unusual properties observed in these materials upon doping, such as high-temperature superconductivity and colossal magnetoresistance.

Atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) imaging of fibrillar J-aggregates of carbocyanine dye 3,3′-bis(γ-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) is performed on mica and glass substrates at room temperature. High resolution AFM imaging reveal that thick fibrils consist of narrow sub-fibrils. A model of an elementary fibril with a cross section 3 × 4 nm2 in size is proposed. The SNOM measurements made in the contact mode indicate the high mechanical strength of the fibrillar J-aggregates.

Atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) imaging of fibrillar J-aggregates of carbocyanine dye 3,3′-bis(γ-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) is performed on mica and glass substrates at room temperature. High resolution AFM imaging reveal that thick fibrils consist of narrow sub-fibrils. A model of an elementary fibril with a cross section 3 × 4 nm2 in size is proposed. The SNOM measurements made in the contact mode indicate the high mechanical strength of the fibrillar J-aggregates.

A model Hamiltonian for centrifugally stabilized electronic-vibrational motion of a cubic perturbed upper "Mexican hat" potential surface for a Mn3+ ion in an octahedral symmetry is formulated, and its eigenspectrum is explored. Theoretically calculated eigenvalues for cubic perturbed ground and excited electronic states are employed to interpret the origin of higher energy narrow side bands (satellite transitions) appearing in the dielectric function spectra of the LaMnO3 complex, which exhibit anomalous temperature dependence in the vicinity of the Neel temperature, TN ≃ 140 K [N. N. Kovaleva et al., J. Exp. Theor. Phys. 122, 890 (2016)].

Retraction of ‘Anomalies in growth of electrodeposited Ni–Fe nanogranular films’ by T. I. Zubar et al., CrystEngComm, 2018, 20, 2306–2315.

By using superconducting quantum interference device (SQUID) magnetometry we investigated anisotropic high-field (H < 7 T) low-temperature (10 K) magnetization response of inhomogeneous nanoisland FeNi films grown by rf sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the percolation transition at the d_c=1.8 nm. We discovered that, beyond conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane magnetization response of the nanoisland FeNi films is not saturated in the range of investigated magnetic fields and exhibits paramagnetic-like behavior. We found that the anomalous out-of-plane magnetization response exhibits an escalating slope with increase in the nominal film thickness from 0.6 to 1.1 nm, however, it decreases with further increase in the film thickness, and then practically vanishes on approaching the FeNi film percolation threshold. At the same time, the in-plane response demonstrates saturation behavior above 1.5-2 T, competing with anomalously large diamagnetic-like response, which becomes pronounced at high magnetic fields. It is possible that the supported-metal interaction leads to the creation of a thin charge-transfer (CT) layer and a Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system with nanoscale circular domains, the observed anomalous paramagnetic-like magnetization response can be associated with a large orbital moment of the localized electrons. The observed magnetization response is determined by the interplay between the paramagnetic- and diamagnetic-like contributions., 11 pages, 7 figures. Section Discussion in more detail, experimental results unchanged. Accepted for publication, Journal of Nanoparticles Research

We use the Mott-Littleton approach to evaluate polarisation energies in LaMnO$_3$ lattice associated with holes localized on both Mn$^{3+}$ cation and O$^{2-}$ anion. The full (electronic and ionic) lattice relaxation energy for a hole localized at the O-site is estimated as 2.4 eV which is appreciably greater than that of 0.8 eV for a hole localized at the Mn-site, indicating on the strong electron-phonon interaction in the former case. Using a Born-Haber cycle we examine thermal and optical energies of the hole formation associated with electron ionization from Mn$^{3+}$, O$^{2-}$ and La$^{3+}$ ions in LaMnO$_3$ lattice. For these calculations we derive a phenomenological value for the second electron affinity of oxygen in LaMnO$_3$ lattice by matching the optical energies of La$^{4+}$ and O$^-$ hole formation with maxima of binding energies in the experimental photoemission spectra. The calculated thermal energies predict that the electronic hole is marginally more stable in the Mn$^{4+}$ state in LaMnO$_3$ host lattice, but the energy of a hole in the O$^-$ state is only higher by a small amount, 0.75 eV, rather suggesting that both possibilities should be treated seriously. We examine the energies of a number of fundamental optical transitions, as well as those involving self-trapped holes of Mn$^{4+}$ and O$^-$ in LaMnO$_3$ lattice. The reasonable agreement with experiment of our predicted energies, linewidths and oscillator strengths leads us to plausible assignments of the optical bands observed. We deduce that the optical band near 5 eV is associated with O(2p) - Mn(3d) transition of charge-transfer character, whereas the band near 2.3 eV is rather associated with the presence of Mn$^{4+}$ and/or O$^-$ self-trapped holes in non-stoichiometric LaMnO$_3$ compound., Comment: 18 pages, 6 figures, it was presented partially at SCES-2001 conference in Ann Arbor, Michigan

© Published under licence by IOP Publishing Ltd.Materials, consisting of Jahn-Teller (JT) ions, such as cuprates and manganites, display many outstanding properties, including high temperature superconductivity and colossal magnetoresistance. There, the role of JT effect, although widely recognized, is still elusive. Here we show that these materials have vibronic excitations, related to local deformations rotating around JT ions in the dynamic limit, arising from linear electron-vibrational coupling in the "Mexican hat" potential profile. Their energy depends on total angular momentum, which is quantized, as in quantum rotors. We found them in the representative JT compound of orthorhombic manganites, LaMnO3. Since the "Mexican hat" potential energy surface is double-valued, they show up near the ground and excited states of JT ions. Recently, by using spectroscopic ellipsometry technique, we showed that they appear in the excited state in the form of sidebands, accompanying the electron transition between the JT split orbitals at neighboring Mn3+ ions. Here, by using Raman scattering technique, we show that they also exist near the ground state. The found quantum rotor excitations may play an important role in many unusual properties observed in these materials.

The multi-order Raman scattering is studied up to a fourth order for a detwinned LaMnO_3 crystal. Based on a comprehensive data analysis of the polarisation-dependent Raman spectra, we show that the anomalous features in the multi-order scattering could be the sidebands on the low-energy mode at about 25 cm-1. We suggest that this low-energy mode stems from the tunneling transition between the potential energy minima arising near the Jahn-Teller Mn3+ ion due to the lattice anharmonicity, and the multi-order scattering is activated by this low-energy electronic motion. The sidebands are dominated by the oxygen contribution to the phonon density-of-states, however, there is an admixture of an additional component, which may arise from coupling between the low-energy electronic motion and the vibrational modes., Comment: 12 pages, 4 figures

The infrared reflectivity of a La_(0.67)Ca_(0.33)MnO_3 single crystal is studied over a broad range of temperatures (78–340 K), magnetic fields (0–16 T), and wave numbers (20–9000cm^(-1)). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000cm-1 in the ferromagnetic state below the Curie temperature T_C=307K. Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near T_C.

The effect of photoinduced reversible coloration was discovered and investigated in superionic RbAg 4 I 5 crystals exposed to light irradiation 2.92 eV ≤ hv ≤ E g = 3.2 eV at T = 300 K . Spectral efficiency measurements of the photoinduced effect let to the discovery that profound changes in the absorption spectrum of RbAg 4 I 5 crystals are observed on 2.92 eV light irradiation. Relaxation of the photoinduced absorption after cessation of the irradiation was found to be of exponential form with a time constant of about 900 s. The mechanism of the photoinduced coloration is considered to be due to self-trapped holes injection under the irradiation of RbAg 4 I 5 superionic crystals.

A new phenomenon of a reversible photoinduced coloration caused by light irradiation is discovered and investigated in superionic RbAg 4 I 5 crystals. The reversible photoinduced absorption is found to be a result of irradiation by light with wavelengths in the region from 420 nm to 450 nm. The proposed mechanism of the discovered effect is associated with ambipolar diffusion of screened by mobile ions optically excited electronic carriers. The processes of color centers creation in superionic crystals RbAg 4 I 5 due to additive coloring in iodine vapours, ionic implantation and γ-ray irradiation are considered.

We have observed a new phenomena of photoinduced transformation of Raman scattering and photoluminescence spectra in RbAg 4 I 5 superionic crystal. A reversible change of the fine structure in Raman spectra at low temperature and reversible change of the concentration of luninescence centers due to irradiation of sample have been studied. Both of these processes are due to the change of local concentration of mobile silver ions in irradiated region of RbAg 4 I 5. The mechanism of interaction between nonequilibrium electrons and silver disordered ionic sublattice has been proposed. The excess concentration of electrons gives rise to diffusion flow of electrons and ions from irradiated region.

Magnetic materials are usually divided into two classes: those with localised magnetic moments, and those with itinerant charge carriers. We present a comprehensive experimental (spectroscopic ellipsomerty) and theoretical study to demonstrate that these two types of magnetism do not only coexist but complement each other in the Kondo-lattice metal, Tb2PdSi3. In this material the itinerant charge carriers interact with large localised magnetic moments of Tb(4f) states, forming complex magnetic lattices at low temperatures, which we associate with self-organisation of magnetic clusters. The formation of magnetic clusters results in low-energy optical spectral weight shifts, which correspond to opening of the pseudogap in the conduction band of the itinerant charge carriers and development of the low- and high-spin intersite electronic transitions. This phenomenon, driven by self-trapping of electrons by magnetic fluctuations, could be common in correlated metals, including besides Kondo-lattice metals, Fe-based and cuprate superconductors., 30 pages, 6 Figures

We have observed a new phenomena of photoinduced transformation of Raman scattering and photoluminescence spectra in RbAg 4 I 5 superionic crystal. A reversible change of the fine structure in Raman spectra at low temperature and reversible change of the concentration of luminescence centers due to irradiation of sample have been studied. Both of these processes are due to the change of local concentration of mobile silver ions in irradiated region of RbAg 4 I 5 . The mechanism of interaction between nonequilibrium electrons and silver disordered ionic sublattice has been proposed. The excess concentration of electrons gives rise to diffusion flow of electrons and ions from irradiated region. A creation of hole trapped centers in irradiated region of γ-RbAg 4 I 5 puts additional constraints on Ag site occupancy. Therefore, for irradiated γ-RbAg 4 I 5 , a “random tetrahedral” model has been used to describe a reversible change of the fine structure in Raman spectra at low temperature.

We have performed ellipsometric measurements of the infrared dielectric response of RuSr2GdCu2O8 polycrystalline ceramics. The transformation of the Cu–O bending phonon mode at 288 cm −1 in the normal state to a broad absorption band at 308 cm −1 in the superconducting state has been observed. This observation strikingly resembles the c-axis optical conductivity data reported for the YBa2Cu3O6.45 crystals. The anomalous softening of the Ru-related phonon mode at 190 cm−1 has been observed on decreasing temperature below the magnetic TM=133 K transition temperature.

Using the Mott–Littleton approach we examine the energies of a number of fundamental optical transitions, as well as those involving self-trapped holes of Mn4+ and O− in LaMnO3 lattice. The reasonable agreement with the experiment of our predicted energies, linewidths and oscillator strengths leads us to plausible assignments of the optical bands observed. We deduce that the optical band near 5 eV is associated with O(2p)–Mn(3d) transition of charge-transfer character, whereas the band near 2.3 eV is rather associated with the presence of Mn4+ and/or O− self-trapped holes in the as-grown non-stoichiometric LaMnO3 compound. We do not exclude other contributions to the latter band.

We present a comprehensive ellipsometric study of an untwinned, nearly stoichiometric LaMnO 3 crystal in the spectral range 1.2–6.0 eV at temperatures 20≤T≤300 K . The complex dielectric response along b and c axes of the Pbnm orthorhombic unit cell, e b (ν) and e c (ν) , is highly anisotropic over the spectral range covered in the experiment. The difference between e b (ν) and e c (ν) increases with decreasing temperature, and the gradual evolution observed in the paramagnetic state is strongly enhanced by the onset of A -type antiferromagnetic long-range order at T N =139.6 K . In this study we focus on the analysis of excitations observed at high energy (∼4–5 eV) and show that the observed temperature changes of their spectral weight are opposite to those found for the lowest-energy gap excitation at ∼2 eV . We used a classical dispersion analysis to quantitatively determine the temperature-dependent optical spectral-weights shifts between low- and high-energy optical bands. Based on the observation of a pronounced spectral-weight transfer between both features upon magnetic ordering, they are assigned to high-spin and low-spin intersite d 4 d 4 ⇌d 3 d 5 transitions by Mn electrons. The anisotropy of the lowest-energy optical band and the spectral-weight shifts induced by antiferromagnetic spin correlations are quantitatively described by an effective spin-orbital superexchange model. An analysis of the multiplet structure of the intersite transitions by Mn e g electrons allowed us to estimate the effective intra-atomic Coulomb interaction, the Hund exchange coupling, and the Jahn-Teller splitting energy between e g orbitals in LaMnO 3 , as well as to extract experimental information concerning the type of orbital order in LaMnO 3 . This study identifies the lowest-energy optical transition at ∼2 eV as an intersite d-d transition whose energy is substantially reduced compared to that obtained from the bare intra-atomic Coulomb interaction.

A comprehensive ellipsometric study was performed on ${\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$ single crystals in the spectral range from 0.01 to 6.2 eV. Direct and indirect band gaps of 73 and 10 meV, respectively, were observed in FeSi at 7 K. One of four infrared-active phonons that is energetically close to the direct absorption edge is coupled both to the electrons and to the low-energy phonon. This is evident from asymmetry in the phonon line shape and a reduction in its frequency when the absorption edge shifts across the phonon energy due to the temperature dependence of the direct band gap. As the temperature increases, the indirect gap changes sign, which manifests as a transition from a semiconductor to a semimetal. The corresponding gain of the spectral weight at low energies was recovered within an energy range of several eV. The present findings strongly support the model indicating that ${\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$ can be well described in an itinerant picture, taking into account self-energy corrections.

The anisotropic complex dielectric response was accurately extracted from spectroscopic ellipsometry measurements at phonon frequencies for the three principal crystallographic directions of an orthorhombic $(Pbnm)$ ${\text{YTiO}}_{3}$ single crystal. We identify all 25 infrared-active phonon modes allowed by symmetry $7{B}_{1u}$, $9{B}_{2u}$, and $9{B}_{3u}$ polarized along the $c$, $b$, and $a$ axes, respectively. From a classical dispersion analysis of the complex dielectric functions $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{ϵ}(\ensuremath{\omega})$ and their inverses $\ensuremath{-}1/\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{ϵ}(\ensuremath{\omega})$, we define the resonant frequencies, widths, and oscillator strengths of the transverse-optical (TO) and longitudinal-optical phonon modes. We calculate eigenfrequencies and eigenvectors of ${B}_{1u}$, ${B}_{2u}$, and ${B}_{3u}$ normal modes and suggest assignments of the TO phonon modes observed in our ellipsometry spectra by comparing their frequencies and oscillator strengths with those resulting from the present lattice-dynamics study. Based on these assignments, we estimate dynamical effective charges of the atoms in the ${\text{YTiO}}_{3}$ lattice. We find that in general, the dynamical effective charges in ${\text{YTiO}}_{3}$ lattice are typical for a family of perovskite oxides. By contrast to a ferroelectric ${\text{BaTiO}}_{3}$, the dynamical effective charge of oxygen related to a displacement along the $c$ axis does not show the anomalously large value. At the same time, the dynamical effective charges of Y and $ab$ plane oxygen exhibit anisotropy, indicating a strong hybridization along the $a$ axis.

The effect has been studied of additive coloring on the magnitude of ion conductivity of RbAg4I5 crystals. It has been found that slight changes of silver stoichiometry of 10−3 at.% can lead to considerable variations of the ionic conductivity Δ[sgrave]i/[sgrave]i ≃ 0.1. The dependence has been observed of the magnitude of ion conductivity on the ratio between the integral intensities of the main bands in the photoluminescence spectrum of the γ-phase of RbAg4I5 which associated with the luminescence centres containing vacancies and interstitials of silver cations.

Spectroscopic ellipsometry is used to determine the dielectric function of the superconducting LaFeAsO$_{0.9}$F$_{0.1}$ ($T_c$ = 27 K) and undoped LaFeAsO polycrystalline samples in the wide range 0.01-6.5 eV at temperatures 10 $\leq T \leq$ 350 K. The free charge carrier response in both samples is heavily damped with the effective carrier density as low as 0.040$\pm$0.005 electrons per unit cell. The spectral weight transfer in the undoped LaFeAsO associated with opening of the pseudogap at about 0.65 eV is restricted at energies below 2 eV. The spectra of superconducting LaFeAsO$_{0.9}$F$_{0.1}$ reveal a significant transfer of the spectral weight to a broad optical band above 4 eV with increasing temperature. Our data may imply that the electronic states near the Fermi surface are strongly renormalized due to electron-phonon and/or electron-electron interactions., 4 pages, 4 figures, units in Fig.2 added

The thermodynamic properties of the ferromagnetic perovskite YTiO$_3$ are investigated by thermal expansion, magnetostriction, specific heat, and magnetization measurements. The low-temperature spin-wave contribution to the specific heat, as well as an Arrott plot of the magnetization in the vicinity of the Curie temperature $T_C\simeq27$ K, are consistent with a three-dimensional Heisenberg model of ferromagnetism. However, a magnetic contribution to the thermal expansion persists well above $T_C$, which contrasts with typical three-dimensional Heisenberg ferromagnets, as shown by a comparison with the corresponding model system EuS. The pressure dependences of $T_C$ and of the spontaneous moment $M_s$ are extracted using thermodynamic relationships. They indicate that ferromagnetism is strengthened by uniaxial pressures $\mathbf{p}\parallel \mathbf{a}$ and is weakened by uniaxial pressures $\mathbf{p}\parallel \mathbf{b},\mathbf{c}$ and hydrostatic pressure. Our results show that the distortion along the $a$- and $b$-axes is further increased by the magnetic transition, confirming that ferromagnetism is favored by a large GdFeO$_3$-type distortion. The c-axis results however do not fit into this simple picture, which may be explained by an additional magnetoelastic effect, possibly related to a Jahn-Teller distortion., Comment: 12 pages, 13 figures

The effect of additive coloring on the magnitude of ion conductivity of RbAg 4 I 5 crystals has been studied. It has been found that slight changes of silver stoichiometry of 10 −3 at.% can lead to considerable variations of the ionic conductivity Δσ i /σ i ⋍0.1 . The dependence has been observed of the magnitude of ion conductivity on the ratio between the integral intensities of the main bands in the photoluminescence spectrum of the γ-phase of RbAg 4 I 5 which associated with the luminescence centres containing vacancies and interstitials of silver cations.

We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO_3 single crystal with ferromagnetic Curie temperature T_C = 30 K. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and 3.7 eV. Although the optical conductivity spectra are only weakly temperature dependent below 300 K, we are able to distinguish high- and low-temperature regimes with a distinct crossover point around 100 K. The low-temperature regime in the optical response coincides with the temperature range in which significant deviations from Curie-Weiss mean field behavior are observed in the magnetization. Using an analysis based on a simple superexchange model, the spectral weight rearrangement can be attributed to intersite d_i^1d_j^1 \longrightarrow d_i^2d_j^0 optical transitions. In particular, Kramers-Kronig consistent changes in optical spectra around 2.9 eV can be associated with the high-spin-state (^3T_1) optical transition. This indicates that other mechanisms, such as weakly dipole-allowed p-d transitions and/or exciton-polaron excitations, can contribute significantly to the optical band at 2 eV. The recorded optical spectral weight gain of 2.9 eV optical band is significantly suppressed and anisotropic, which we associate with complex spin-orbit-lattice phenomena near ferromagnetic ordering temperature in YTiO_3.

We report the dc transport (5 K ≲ T ≲ 380 K) and spectroscopic ellipsometry (0.8 eV ≤ hν ≤ 8.5 eV, T ≃ 300 K) study of β-Ta films prepared by rf sputtering deposition as a function of their thickness in the range 2.5 nm ≲ d ≲ 200 nm. The dc transport of the β-Ta films with a thickness d ≳ 25 nm is characterized by negative temperature coefficient of resistivity (TCR) caused by localization effects peculiar of highly disordered metals. Their dielectric function spectra display non-metallic-like behavior due to the presence of the pronounced band at 2 eV. We found that with increasing TCR absolute value, specifying elevated degree disorder, the optical spectral weight (SW) of free charge carriers decreases. The associated SW is recovered in the range of Mott-Hubbard transitions, indicating the mechanism of localization enhancement by electronic correlations in disordered metals.

The reflectance of La(sub 0.7)Ca(sub 0.3)MnO(sub 3) epitaxial films on perovskite substrates with a range of lattice constants is studied in the frequency range of 50 cm(sup -1) - 5000cm(sup -1). The complex dielectric functions of the bare La(sub 0.7)Ca(sub 0.3)MnO(sub 3) films are obtained by modeling the measured reflectivity spectra of the two-layer La(sub 0.7)Ca(sub 0.3)MnO(sub 3)/substrate system with separaately measured dielectric functions of the bare substrate.

Giant anomalies are found in the temperature dependence of Raman-active phonons in the quantum magnet $\mathrm{TiOCl}$, suggesting the presence of an extended fluctuation regime. This regime coincides with a pseudogap phase identified in earlier NMR experiments. The observed large, local spin-gap is proposed to origin from coupled spin∕lattice fluctuations. Below $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, in the long-range crystallographically distorted phase, a dimerized ground state with a smaller, global spin-gap of about $2{\ensuremath{\Delta}}_{spin}\ensuremath{\approx}430\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ exists. This transition also marks a dimensionality cross-over of the system.

Using spectral ellipsometry, we measured the dielectric function of a Na(0.82(2))CoO2 crystal that exhibits bulk antiferromagnetism with T(N)=19.8 K. We identify two prominent transitions as a function of temperature. The first one at 280 K involves marked changes of the electronic and lattice responses that are indicative of charge ordering in the CoO2 layers. The second transition occurs around T(N)=19.8 K and reveals sizable spin-charge coupling. The data are discussed in terms of charge ordering and formation of magnetopolarons due to a charge-induced spin-state transition of adjacent Co3+ ions.

Spectral ellipsometry is used to determine the dielectric function of an untwinned crystal of LaMnO3 in the range 0.5-5.6 eV at temperatures 50

Spectral ellipsometry is used to determine the dielectric function of an untwinned crystal of LaMnO3 in the range 0.5-5.6 eV at temperatures 50or=Tor=300 K. A pronounced redistribution of spectral weight is found at the Ne el temperature T(N)=140 K. The anisotropy of the spectral weight transfer matches the magnetic ordering pattern. A superexchange model quantitatively describes spectral weight transfer induced by spin correlations. This analysis implies that the lowest-energy transitions around 2 eV are intersite d-d transitions, and that LaMnO3 is a Mott-Hubbard insulator.

The temperature-dependent redistribution of the spectral weight of the CuO 2 plane–derived conduction band of the YBa 2 Cu 3 O 6.9 high-temperature superconductor (superconducting transition temperature = 92.7 kelvin) was studied with wide-band (0.01– to 5.6–electron volt) spectroscopic ellipsometry. A superconductivity-induced transfer of the spectral weight involving a high-energy scale in excess of 1 electron volt was observed. Correspondingly, the charge carrier spectral weight was shown to decrease in the superconducting state. The ellipsometric data also provide detailed information about the evolution of the optical self-energy in the normal and superconducting states.