Dielectric Susceptibility Research Articles

Giant linear magnetoelectric effect at the morphotropic phase boundary of epitaxial Sr0.5Ba0.5MnO3 films

First-principles calculations are conducted to compute linear magnetoelectric coupling coefficients in epitaxial (001) ${\mathrm{Sr}}_{0.5}{\mathrm{Ba}}_{0.5}{\mathrm{MnO}}_{3}$ films. A large enhancement of different linear magnetoelectric elements is found in a strained-induced morphotropic phase boundary region. Such enhancement is demonstrated to originate from the behavior of the dielectric susceptibility, thanks to a simple phenomenological model that is presently shown to be relevant and accurate. This work can thus provide a promising approach towards designing highly desired single-phase multiferroic with a colossal magnetoelectric conversion.

Spectral characterization of the Rashba spin-split band in a lead halide perovskite single crystal by photocurrent heterodyne interference spectroscopy

We characterized the temperature dependence of the complex dielectric susceptibility spectrum of a perovskite $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Pb}{\mathrm{Br}}_{3}$ single crystal by using heterodyne interference spectroscopy. Owing to a time-domain measurement that is not influenced by incoherent lattice relaxations, we were able to detect a low-energy indirect-gap band. We observed two peaks in the energy region below the exciton transition at the $R$ point in the imaginary part of the spectrum. The temperature dependences of the energies of these peaks were different from the dependence of the energy of the direct-transition exciton. The trends of both the splitting width and peak intensities can be explained by assuming a Rashba spin-split band.

Evolution of the structural, magnetic, and electronic properties of the triple perovskite Ba3CoIr2O9

We report a comprehensive investigation of the triple perovskite iridate Ba$_{3}$CoIr$_{2}$O$_{9}$. Stabilizing in the hexagonal $P6_{3}/mmc$ symmetry at room temperature, this system transforms to a monoclinic $C2/c$ symmetry at the magnetic phase transition. On further reduction in temperature, the system partially distorts to an even lower symmetry ($P2/c$), with both these structurally disparate phases coexisting down to the lowest measured temperatures. The magnetic structure as determined from neutron diffraction data indicates a weakly canted antiferromagnetic structure, which is also supported by first-principles calculations. Theory indicates that the Ir$^{5+}$ carries a finite magnetic moment, which is also consistent with the neutron data. This suggests that the putative $J=0$ state is avoided. Measurements of heat capacity, electrical resistance noise and dielectric susceptibility all point towards the stabilization of a highly correlated ground state in the Ba$_{3}$CoIr$_{2}$O$_{9}$ system.

NLO evaluation on opto-electronic application and chemical potential oscillation analysis of 2-Chloro-4-nitro-N-methylaniline crystal using crystallographic, spectroscopic and theoretical tools

The new organic composite crystal was grown from 2-Chloro-4-nitro-N-methylaniline compound using Bridgman method and the grown crystal was characterized morphologically, optically, opto-electronically using suitable analytical tools. All the theoretical data were obtained for interpreting physical, chemical and optical characteristics of chemical species- crystal by performing different types of calculations. The crystal dimensions were measured as 0.19 × 0.68 × 0.38 mm3 and the Birefringence (Δn) Kλ/t was calculated to be 1.02. The nonlinear coefficient and nonlinear optical (NLO) efficiency were calculated as 0.8381 at 6.81pm/V. The FT-Raman and FT-IR vibrational data were evaluated to find the scattering bond lengths and bond angles and the homogeneity and heterogeneity of the bond profile was checked for estimating dielectric susceptibility. The chemical shift results for core as well as allied carbons are assessed and the delocalization of chemical potential on different atomic nodal regions was keenly studied. The dielectric property inducement over the molecule and crystal structure was monitored and the direct band gap for amplifying the optical energy was noted and the band gap tuning was discussed. The physico-chemical parameters were evaluated and the support of such parameters was tested. The geometrical parameters were evaluated and the optimized bond lengths and bond angles were checked for customizing trans free structure for constructing prearranged crystal. The UV-Visible absorption and transmission spectral data was evaluated to find the CT complex of the compound. The vibrational circular dichroism (VCD) spectral sequence was thoroughly checked for identifying the important dipole and polarized bonds for fixing enantiomer characteristics.

Description of intermodulation generation of nonlinear responses beyond the validity of the power series expansion

Weakly nonlinear responses are commonly described by a power series expansion. However, intermodulation distortion products that cannot be described by a power series have been observed in a variety of physical systems. As the power series description is only applicable within its radius of convergence, we choose an alternative approach based on Fourier coefficients to describe intermodulation levels beyond the convergence of the power series. The description over a wide power range allows us to make a decision about models and to determine previously inaccessible model parameters. We apply the approach to data obtained from the characterization of the nonlinear dielectric susceptibility of a glass ceramic in the microwave range. The data are accurately modeled by a saturable absorber's response. We obtain the absorber's linear contribution to the polarization (χ1=10−5) as well as its characteristic ratio of nonlinear and linear polarization (χ3/χ1=10−9 m2/V2). Due to the small contribution of the saturable absorber to the overall polarization, the material shows a highly linear response (χ3=10−14 m2/V2).

Realizing negative index of refraction in an ensemble of ground-state polar molecules with lasers

We propose a coherent optical method for creating negative refractive index (NRI) for a gaseous ensemble of ground-state polar molecules possessing both permanent electric and magnetic moments. Exploiting the pure rotational transition between the two lowest rotational levels of the ground vibrational state one can generate two dressed states of mixed parity using a microwave laser. These dressed states are then used as the two lower states of a Λ-type three-level scheme using two infrared lasers to couple them to another ro-vibrational level in the ground-state manifold. One of the infrared lasers is used as a weak probe and the other as a control field with a fixed detuning. We take into account local-field effects on the dielectric response of the medium at the probe frequency in terms of Clausius–Mossoti relation. We extract magnetic response out of purely dielectric response and calculate the magnetic permeability of the medium in terms of dielectric susceptibility. Our results show that there is a small frequency window near the two-photon resonance where both electric permittivity and magnetic permeability are negative with vanishingly small absorption. The figure of merit for the medium is shown to exceed unity. We interpret our results in terms of the proximity of EIT and quantum interference. We discuss the possible realization of our method using cold polar molecules that are recently experimentally produced.

Exploring the Possibility of Surface Change during Emission of Radiation for the Electron

We assume from previous work that the mass of the electron creates a spacetime curvature thus giving a picture of local change of volume and surface. The assumption comes from the relativistic radius of the electron which gives as a first estimate for a spacetime curvature. The volume created seems to be depending on the dielectric susceptibility which alters the speed of light thus creating a new metric. We find a formula for this new volume and the rate of change of the surfaces locally.

Physical and optical analysis of Sm3+ doped zinc phosphate glass

Sm3+ (0.1, 0.2, 0.3, 0.4 & 0.5 wt%) doped zinc phosphate glasses have been prepared by melt quenching technique. Their physical, as well as optical properties, have been studied. The UV–Vis absorption spectroscopy was carried on in the wavelength range of 400–700 nm which reveals five absorption bands at 406 nm, 445 nm, 478 nm, 533 nm, and 572 nm respectively. The direct bandgap is found to be 2.42–2.47 eV while the indirect bandgap is 2.30–2.34 eV. Urbach energy is calculated to be 0.4237–0.4445 eV. The other parameters like dielectric susceptibility, metallization, refractive index, oxygen packing density, etc., have also been studied.

Наведенное двулучепреломление в квантовых точках CdSe в матрице фосфатного стекла

In this paper, we report on the experimental observation of light-induced anisotropy (the optical Kerr effect) due to third-order nonlinear dielectric susceptibility (3) in a nanocomposite material consisting of CdSe quantum dots in a phosphate glass matrix. The signs and values of the off-diagonal components of the tensor (3) are determined using z-scanning techniques and nonlinear ellipsometry. It was shown that the nonlinear response contains three time components, the fastest of which does not exceed 20 ps, the average has an exponential form and amounted to 90 11 and 38530 ps for different samples, and the longest nonexponential and amounts to times of the order of a few nanoseconds. The switching of an optical signal with a time not exceeding 20 ps is demonstrated.

Генерация второй гармоники-суммарной частоты в тонком сферическом слое. I. Аналитическое решение

The problem of the simultaneous second–harmonic and sum–frequency generation by two coherent plane electromagnetic waves with elliptical polarizations and equal frequencies in a thin spherical layer is solved in the Rayleigh–Gans–Debye model. The second–order dielectric susceptibility tensor is chosen in a form containing four independent components (including one chiral component). Fundamental differences are shown between the problem statements as well as between solutions to the problem of second–order nonlinear generation by several coherent electromagnetic waves and the problem of sum–frequency generation in the limiting case of equality of the frequencies of the incident waves. Combinations of parameters are determined at which the spatial distribution of the radiation generated as a result of incidence of two plane waves coincides with the distribution of second–harmonic radiation generated by one plane wave. The limiting cases of the obtained solution are considered: small and large radii of the spherical particle. In these cases the contributions of the chiral and non-chiral anisotropy coefficients to the generated radiation are determined.

Mechanical and Electronic Properties of CeO <sub>2</sub> Under Uniaxial Tensile Loading: A DFT Study

CeO2 is a promising candidate for materials utilized in solid oxide fuel cells (SOFCs) due to its high ionic conductivity. The high operating temperature of SOFCs results in residual thermal stress in the materials. In this work, for the first time, we studied simultaneously the mechanical and electronic behavior of CeO2 under different uniaxial tensile loading directions using density functional theory. CeO2 shows strong anisotropic mechanical and electronic behavior under uniaxial tensile strain that it has the highest ideal strength and fracture strain along [100] direction. Meanwhile, [100] tensile strain also leads to the largest band gap reduction compared with the other two strain directions. The analysis of the mechanism shows that the highest strength along [100] direction is from the highest Young’s modulus and surface energy. While the analysis on the band gap variation using a theoretical model previously developed by us suggest that the largest average bond length and dielectric susceptibility variation leads to the largest band gap reduction when [100] tensile strain is applied to CeO2. Therefore, the current study provides a meaningful insight into the mechanical and electronic properties of CeO2 under stress, which is vital for its application as SOFCs’ materials.

Investigation of domain structure in ferroelectric thin films by means of the Ising model

The domain structure in thin ferroelectric films was investigated in the framework of the modified Ising model with short-range exchange and long-range dipole-dipole interactions. The depolarizing field was also taken into account for the study of size effects in thin films. This field is the dominant factor influencing on the existence of phase transitions in the films. We used Monte Carlo method with the standard Metropolis algorithm to generate configurations on three-dimensional cubic lattices. The domains sizes were calculated in the longitudinal and transverse directions relatively to the spontaneous polarization direction. Temperature dependences of the domain sizes are obtained for different values of interaction constants. It was proved that the introduction of the depolarizing field leads to the appearance of a dead layer on the film boundaries. The dead layer thickness increases with increasing temperature. At a certain temperature (not equal to the Curie temperature), the dead layer is destroyed. The temperature dependences of the dielectric susceptibility at different film thicknesses have been calculated. It was shown that these dependencies have two maxima. The first maximum corresponds to a phase transition, the second one exists only for only thin films and corresponds to the destruction of the dead layer.

Генерация второй гармоники-суммарной частоты в тонком сферическом слое: III. Свойства решения

Mathematical properties of functions characterizing symmetries of spatial distribution of second harmonic–sum frequency radiation are determined. The conditions at which there occurs no generation and the conditions at which the polarization of the generated radiation is linear are found. The revealed properties are systematized by their manifestations in the directivity patterns of the generated radiation. Methods based on these properties for determining the components of the nonlinear dielectric susceptibility tensor are proposed. The relationship is described between the revealed properties as well as conditions and previously found similar properties and conditions for the phenomena of second–harmonic generation and sum–frequency generation.

Chemical Additive Cascading System – A new Scheme for Enhancing Optical Nonlinearity

Nanophotonics is an emerging area where nanotechnology is used to change the physical and chemical properties of photonic materials or the effectiveness of photonic processes that have major applications in optical communication and computation. Though many photonic devices are developed using nonlinear optical materials, efforts are still going on to increase their efficiency toward 100% and other device characteristics toward their optimum level. In order to improve the efficiency of the third harmonic process further, we have a plan to use dye-sensitized metal nanoparticles doped in PMMA films. It is expected that the ability of nanotechnology in tailoring the physio-chemical properties of the materials will give rise to the optimum nonlinear devices to be used in nanophotonics. A considerable improvement in both nonlinear optical susceptibility and laser damage threshold is expected based on the results published in the case of dye-sensitized metal nanoparticle doped solar cells. Such a research may contribute to the efficient nanophotonic devices such as all optical switches, which are the basic building blocks of the final dream of realizing all optical computers. In this paper, a theoretical study is carried out on the effect of sensitization of some well-known nanocomposites TiO2/Au and ZnS/PVA by nonlinear DASPB dye-doped PMMA-MA polymer matrix in order to change the dielectric and nonlinear susceptibility. This is achieved by the systematic study of the size of nanoparticles used for the sensitization study, various donor-acceptor combinations, and concentration of dyes & nanoparticles in the sample films. The nonlinear absorption coefficient for each case and the theoretical optical limiting properties are expected to be modified based on cascaded nonlinear susceptibility for Type 1, Type 2, and Type 3 Z-scan configurations.

Strong Coupling of Exciton-Polaritons in a Bulk GaN Planar Waveguide: Quantifying the Coupling Strength

We investigate the demonstration and quantification of the strong coupling between excitons and guided photons in a GaN slab waveguide. The dispersions of waveguide polaritons are measured from T=6~K to 300~K through gratings. They are carefully analyzed within four models based on different assumptions, in order to assess the strong coupling regime. We prove that the guided photons and excitons are strongly coupled at all investigated temperatures, with a small $(11 \%)$ dependence on the temperature. However the values of the Rabi splitting strongly vary among the four models: the "coupled oscillator" model over-estimates the coupling; the analytical "Elliott-Tanguy" model precisely describes the dielectric susceptibility of GaN near the excitonic transition, leading to a Rabi splitting equal to $82 \pm 10 \ meV$ for TE0 modes; the experimental ellipsometry-based model leads to smaller values of $55 \pm 6 \ meV.$ We evidence that for waveguides including active layers with large oscillator strengths, as required for room-temperature polaritonic devices, a strong bending of the modes dispersion is not necessarily the signature of the strong-coupling, which requires for its reliable assessment a precise analysis of the material dielectric susceptibility.

Non-linearity in engineered lead magnesium niobate (PbMg1/3Nb2/3O3) thin films

The local compositional heterogeneity associated with the lack of long-range ordering of Mg2+ and Nb5+ in PbMg1/3Nb2/3O3 (PMN) is correlated with its characteristic “relaxor” ferroelectric behavior. Earlier work [Shetty et al., Adv. Funct. Mater. 29, 1804258 (2019)] examined the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg2/3Nb1/3)O3 and PbNbO3, as suggested by the “random-site model.” This work confirmed the development of ferroelectric domains below 150 K in long-range-ordered films, epitaxially grown on (111) SrTiO3 substrates using alternate target timed pulsed-laser deposition of Pb(Mg2/3Nb1/3)O3 and PbNbO3 targets with 20% excess Pb. In this work, the first through third-harmonic dielectric charge displacement densities and complex dielectric susceptibilities were analyzed as a function of temperature and frequency in zero-field-cooled PMN films with short- and long-range ordering. The long-range ordering decreased the dispersion in the first- and third-harmonic dielectric charge displacement densities relative to short-range-ordered films. It was found that the one-dimensional ordering achieved in the long-range-ordered film is insufficient to achieve a fully normal ferroelectric state. In the presence of quenched random electric fields, these films require a small ac field to facilitate percolation of the polar nano-regions, enabling normal ferroelectric-like behavior at lower temperature (T < 240 K). The films behave like a typical relaxor near room temperature. With reduced ordering, the short-range films exhibit greater dispersion in linear and higher order harmonic dielectric charge displacement density.

Molecular-Theory of High Frequency Dielectric Susceptibility of Nematic Nanocomposites

A molecular-statistical theory of the high frequency dielectric susceptibility of the nematic nanocomposites has been developed and approximate analytical expressions for the susceptibility have been obtained in terms of the effective polarizability of a nanoparticle in the nematic host, volume fraction of the nanoparticles and the susceptibility of the pure nematic phase. A simple expression for the split of the plasmon resonance of the nanoparticles in the nematic host has been obtained and it has been shown that in the resonance frequency range the high frequency dielectric anisotropy of the nanocomposite may be significantly larger than that of the pure nematic host. As a result, all dielectric and optical properties of the nanocomposite related to the anisotropy are significantly enhanced which may be important for emerging applications. The components of the dielectric susceptibility have been calculated numerically for particular nematic nanocomposites with gold and silver nanoparicles as functions of the nanoparticle volume fraction and frequency. The splitting of the plasmon resonance has been observed together with the significant dependence on the nanoparticle volume fraction and the parameters of the nematic host phase.

Effect of electrode on dielectric susceptibility and pyroelectric properties of a ferroelectric thin film capacitor using landau-khalatnikov theory

The influence of electrodes on the dielectric susceptibility and pyroelectric properties of a ferroelectric thin film with surface transition layers has been investigated within the framework of Landau-Khalatnikov dynamic theory. The contribution of the electrodes is reflected by the depolarization field in the free-energy function. The large electrode effect implies the strong depolarization field in ferroelectric thin films. The results show that the electrode materials can greatly impact the dynamic dielectric and pyroelectric properties of a ferroelectric thin film.

Few-cycle optical pulses in negative index materials with dispersive permittivity and permeability

Propagation of few-cycle optical pulses in nonlinear optical Kerr (cubic) and non-Kerr (quintic) type metamaterials, exhibiting frequency-dependent dielectric susceptibility and magnetic permeability, is considered. Considering the theory of electromagnetic waves from Maxwell’s equations, a new nonlinear evolution equation describing the combined influences of higher-order nonlinearities and higher-order linear and nonlinear dispersions, appropriate for electromagnetic ultrashort pulse propagation in negative index materials, is derived beyond the slowly varying envelope approximation. A fully numerical simulation of the newly derived model equation, based on the lossy Drude model, shows the propagation of soliton-like stable few-cycle optical pulses under some parameter values. The change in types of self-steepening parameters induces structural changes of the initial input pulse, characterized by a soliton molecule made of either asymmetric or symmetric optical pulses. Also, the mutual balancing between Kerr and non-Kerr nonlinearities and higher-order dispersions is found to support the formation of soliton-molecules in both the normal and anomalous group velocity dispersion regimes.

Optical and electronic properties for As-60 at.% S uniform thickness of thin films: Influence of Se content

Abstract Thin films of As40S60-xSex ((0 ≤ x ≥ 60) at. %) have been efficiently synthesized through the process of vacuum thermal evaporation. The present framework analyzes the thin films to determine both optical and electronic parameters as a function of change of Se concentrations. The thickness of the obtained films, d have been mathematically determined utilizing Swanepoel's computations and experimentally via an MII-4 interference microscope with an accuracy of 1%. The thickness of the studied films has been closed to 500 ± 15 nm. Additionally, the optical properties of these films have been scrutinized from the transmittance and reflectance spectra measured by a UV–Vis–NIR spectrophotometer. The transmission spectra, T (λ) of such films have been documented in the spectral region 400–2500 nm. Based on the optical measurements, all of the linear optical constants, the linear optical and dielectric parameters, the linear and non-linear optical susceptibility criteria, and the material dispersion coefficient M ( λ ) have been computed. Besides, the nonlinear refractive index, energies of the electronic polarization have been determined.