Новые публикации

https://doi.org/10.1134/S0030400X25700092

The characteristics of a planar optical resonator made of quartz glass surrounded by silver mirrors have been studied when their thickness was varied. The frequency responses of band-pass filters on planar structures obtained by vacuum deposition on quartz glass (SiO₂) substrates of three quartz layers, which are half-wavelength resonators separated from each other, from the substrate, and from the free space by four layers of silver (Ag), were measured. The thicknesses of the Ag and SiO₂ layers were determined on the basis of the specified filter passband parameters by synthesizing one-dimensional models using electrodynamic analysis. The experimental frequency dependencies of the real and imaginary parts of the complex permittivity of silver have been considered. The measured frequency responses of the manufactured prototypes of red, green, and violet filters are in good agreement with the characteristics obtained during synthesis. Systematic studies of filters with a central passband frequency of 300 THz (wavelength of 1 µm) and a relative bandwidth of 2‒20%, containing from 3 to 6 resonators, have been carried out. The high performance of the developed filters demonstrates their potential for their use in optical devices.

https://doi.org/10.3390/ma18235393

Transparent conductive electrodes that combine flexibility with effective electromagnetic interference (EMI) shielding are important for next-gen flexible electronics and 5G/6G communication devices. Achieving high optical transparency, low sheet resistance, and broadband shielding performance remains a sophisticated task. This work demonstrates a solution: the synthesis and comprehensive characterization of flexible In₂O₃/Ag/In₂O₃ (IAI) structures on polyethylene terephthalate substrates. The optimized structure with a 13.2 ± 1.1 nm silver interlayer achieves an incredible combination of properties: high optical transmittance (82.59% at 500 nm), low sheet resistance (6.4 ± 0.8 Ω/sq), and insignificant optical haze (1.04%). Broadband EMI shielding measurements from 10 MHz to 1 THz reveal a uniform shielding effectiveness of 25–30 dB across band from radiowave to terahertz. The IAI structures also show outstanding mechanical resilience, maintaining their electrical and shielding performance under repeated bending. This unique set of attributes positions IAI thin films as a prospective material for transparent EMI shielding in advanced telecommunications and flexible optoelectronics.

DOI https://doi.org/10.1039/D5TC03097H

Single crystals of the solid solutions Co₂Co_1−xFe_x(BO₃)O₂ (0.0 < x < 1.0) were grown using flux. The average and local crystal structures were studied using X-ray diffraction and Mössbauer spectroscopy combined with density functional theory calculations. The calculated quadrupole splittings are QS ≈ 1.81–2.60 mm s⁻¹ for the Fe³⁺ ions at the Fe1 and Fe3 positions, QS ≈ 0.92—1.17 mm s⁻¹ at the Fe4 position, QS ≈ 0.50–0.70 mm s⁻¹ at the Fe2 position, and are in quantitative agreement with the experimental values. A detailed analysis revealed that the confined oxygen atoms contribute to the tetragonal distortions of the coordinated octahedra. The large ligand contribution and charge anisotropy due to the covalent admixing of the spin-down 3d orbitals with 2p orbitals of the unconfined oxygen atoms are responsible for the large value of the electric field gradient at Fe1 and Fe3. The cation distribution over the entire series of the solid solution was established, which reflects the order of preference for Fe³⁺ ions: Fe4 ≫ Fe2 > Fe1 ≈ Fe3. A preliminary magnetic study using dc magnetization and heat capacity measurements revealed that the solid solutions undergo magnetic phase transitions at T₁ = 48, 66, and 82 K for x = 0.3, 0.5, and 0.7, respectively. Additional magnetic anomalies are observed upon cooling. The magnetic properties appear to be sensitive to the cation distribution.

https://doi.org/10.1007/s10948-025-07110-7

We study the effect of out-of-plane Zeeman field on zero-energy vortex- and corner-localized excitations in a two-dimensional second-order topological superconductor. It is shown analytically and numerically that zero-energy vortex modes are robust against the Zeeman-field effect as long as superconductivity is not destroyed by the field and a superconducting bulk gap is open. On the other hand, Majorana Kramers pairs existing at each corner of a square lattice at zero field and protected by time-reversal symmetry are gapped, in general, by the field. Despite that, we also found the specific model parameters supporting pairs of Majorana corner modes with zero energy in the presence of a magnetic field. In this parametric regime, the corner modes can coexist with zero-energy vortex modes in the presence of a vortex in the model. The precursor for coexisting zero-energy vortex and corner modes under the Zeeman field is the gapless bulk spectrum with Dirac cones in the normal (nonsuperconducting) state.

https://doi.org/10.1007/s00289-025-06203-6

The aim of this study was to develop polymer microparticles conjugated with type I collagen and loaded with the antiseptic brilliant green (tetraethyl 4,4-diaminotriphenylmethane oxalate) for wound treatment and healing of skin lesions. Microparticles loaded with brilliant green (BG) were synthesized by the emulsification method with the achieved encapsulation efficiency of 95.5%. Collagen was covalently attached to the surface of the polymer microparticles. The average size of the microparticles with deposited antiseptic was 57.2 ± 0.2 μm, and that of the microparticles with collagen was 58.9 ± 0.4 μm. Their respective zeta potential values were − 27.3 mV and − 31.7 mV. Scanning electron microscopy (SEM) showed uniform spherical morphology of the particles. The results of the in vitro release study demonstrated a sustained release of BG for more than 600 h. Moreover, surface modification of the microparticles with type I collagen significantly improved cell adhesion and biocompatibility of the local antiseptic delivery system in NIH/3T3 mouse fibroblast cultures.

https://doi.org/10.1364/JOT.92.000082

This study investigated the spectral properties of silver irregular microgrids (AgIMGs) and sandwich structures in the visible and radio frequency (RF) ranges. AgIMGs were fabricated using a self-assembled template formed by cracking a thin film of egg white. Aim of study. The aim of this study was to develop a method for producing AgIMGs with a thickness exceeding 500 nm, low surface resistance, and high optical transmittance in the visible range. Additionally, sandwich structures based on such microgrids that demonstrate a shielding effectiveness (SE) of at least 60 dB in the RF range were fabricated. Main results. A method for locally peeling off the perimeter (CPP) of self-organized template cells has been developed. It allows for an increase in the thickness of the deposited silver to more than 500 nm. Increasing the thickness of the deposited metal is a critical factor for improving the optoelectric characteristics of AgIMG. Two-layer sandwich structures were obtained based on our AgIMG. Sandwich structures consisting of irregular silver microgrids based on a template with a partially peeled off perimeter of the cells show an SE of 71.01 dB in the range of 1–7 GHz with a transmission value of 80.02% in the visible range. Practical significance. Sandwich structures based on AgIMGs formed on a template with a partially detached cell perimeter are a promising solution for shielding optically transparent objects and information display devices. The sandwich structures developed in this study outperform existing optically transparent RF-shielding screens in terms of the combined parameters of SE, optical transmittance, and production cost.

https://doi.org/10.1364/JOT.92.000138

The rate of electron transfer between plant photosystems based on fluorescence measurements and calculated density graphs of photon processes is studied. Aim of study. The purpose of this paper is to determine how the structural and optical parameters of plants are affected by their growth conditions. Method. The morphology of chloroplasts was examined by electron microscopy of tissue samples of barley flag leaves grown under the same intensity of illumination in a growing chamber and in the field. The samples underwent full preparation for electron microscopy, including staining with heavy metals to increase the contrast, and were analyzed using a Hitachi HT 7700 transmission electron microscope. Chlorophyll fluorescence parameters of the flag leaves were measured in vivo using the LI-6800 photosynthesis system in a closed leaf chamber that included a built-in fluorimeter. Main results. The role of structural coloration caused by interference and diffraction of light on structural elements of a green leaf having a period comparable with the wavelength of light has only been described in recent years. The study also identified a significantly denser and better-ordered grana structure in the chloroplasts of barley leaf cells grown under artificial conditions. Despite this difference, the maximum quantum yield of Photosystem II in both samples lay in the range of values typical for plants in their normal physiological state. Since electron transport is highly dependent on the spatial organization of the photosynthetic apparatus in the chloroplast thylakoid membranes, the denser “packing” of grana will clearly support more efficient electron transport because the molecular complexes involved in the process are closely arranged. We found that the electron transport rate was different for the plants grown in the field and those grown in the chamber. The electron transport rate for the plants grown in the growth chamber was 1.7 times faster than that for plants grown in the field. Thus, numerical calculations and the spectroscopy/electron microscopy results showed a connection between the photon state density, electron transport rate, and the occurrence of chemical reactions during photosynthesis. Practical significance. Comparing the photosynthetic parameters of the same plants grown in different environments provides useful information on the mechanism behind the photosynthesis process. Identification of the main factors (quantity and quality of water, external environment, amount of nutrients, etc.) affecting the structure and optical properties of plants will increase agricultural yields and reduce costs by optimizing resources and technological processes.

https://doi.org/10.1016/j.photonics.2025.101489

We consider spheroidal dielectric microparticles subject to radiation forces and torques induced by two linearly polarized weakly-focused counter-propagating Gaussian beams. Since the symmetry is lifted by the spheroidal shape of the particles the effects of both net radiation force and torque are taken into account. It is found that in the case of oblate spheroids there is a specific ratio of the semi-axes leading to anomalous drift of particles both in the lateral and the longitudinal direction. Such an effect results in displacement from the initial condition by distance up to 70μm.

https://doi.org/10.1016/j.jpcs.2025.113452

In Ni_3–xCo_xB₂O₆ the direction of the easy axis of magnetization changes from the crystallographic direction c to the crystallographic direction b with an increasing concentration of cobalt ions due to the competition of anisotropies and exchange interactions. The theoretical calculations of the orientation of magnetic moments in the Ni_3–xCo_xB₂O₆ solid solutions are in good qualitative agreement with the experimental data. The orientation of magnetic moments is significantly influenced by the spin-orbit interaction of nickel and cobalt ions. In the Ni_2.81Co_0.19B₂O₆ compound two magnetic phase transitions are observed. Moreover, an oblique phase is observed in the concentration range 0.6 < x < 0.93.

https://doi.org/10.1134/S1063784225700409

A channel bandpass filter of the satellite communication multiplexer has been developed around a design consisting of 12 coaxial resonators. To cut the group delay time and considerably improve the selectivity of the device, two additional inductive and two additional capacitive couplings between nonadjacent resonators have been applied. This makes it possible to provide two zero poles near the right and left edges of the passband. To reduce the spread of the passband’s transmission factor, a special method was applied that allows one to somewhat decrease reflection losses near the edges of the bandpass of the filter. This, in combination with the electrodynamic analysis of a 3D model developed for the given design, makes it possible to synthesize a small-size filter with the center frequency of the bandpass f₀ = 4 GHz and its width Δf = 45 MHz measured at a level of 0.8 dB from minimal losses. The measured characteristics of the filter prototype are in good agreement with calculation data.

Full article

Thermoelectric effects in the solid solution Mn_1-xLu_xS (x ≤ 0.2) in a wide temperature range without a field and in a magnetic field of 12 kOe are studied. The temperatures at wich a change in the sign of the thermoelectric power and the maxima of the Seebeck coefficient below Neel temperature in a magnetic field are found. The thermal expansion coefficients are measured to establish a correlation with the thermoelectric power. The thermoelectric power anomalies are explained within the framework of the orbital glass model and a change in the type of magnetic order in a magnetic field in a magnetically ordered region.

https://doi.org/10.3390/molecules30224482

Structure transformations in cholesteric droplets with planar anchoring induced by an electric field are studied experimentally. The radial spherical structure is formed initially, then it transforms into the quasi-nematic untwisting state under the action of an electric field 𝐸 =1.75 V/μm. The dependence of structure transformations on the voltage switching-off mode is examined. At the one-step voltage-off mode, the Lyre structure is realized in cholesteric droplets at the relative chiral parameter in the range 4.3 ≤𝑁 ≤8.5. The axis-symmetric bipolar structure and the low-symmetric planar bipolar structure are obtained at the multi-step voltage-off mode. The possibility of forming such structures and their stability are determined by the type of voltage switching-off mode, the N value, the surface anchoring strength (the value of cholesteric helix pitch), and the presence of the surface point defects.

https://doi.org/10.3390/polym17223064

In this study, we demonstrated chloroprene rubber (CR)-based composites with the addition of synthesized alumina nanofibers (AONF) with a high aspect ratio (>1000). AONF were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). AONF were introduced by pre-dispersion. The resulting chloroprene rubber/aluminum oxide nanofiber (CR/AONF) composites were subjected to tensile and shear adhesive bonding tests. The tensile test results for the CR/AONF composites are 81% greater than those of the original CR composite (0.85 MPa and 1.54 MPa, respectively). Shear adhesive bonding tests were conducted for glass and steel. CR/AONF demonstrates a 213% (for steel) and 262% (for glass) increase in shear strength. The main strengthening mechanisms are reinforcement, CR adsorption on the AONF surface, and crack arrest. These results may expand our understanding of the potential of sealant strengthening using AONF.

https://doi.org/10.3390/molecules30224437

The electrochemical properties of the dysprosium-doped strontium cobaltite SDC (Sr_0.8Dy_0.2CoO_3−δ) were evaluated for possible application as pseudocapacitor electrode materials. Dense perovskite SDC ceramics were prepared using standard solid-state synthesis techniques. The SDC sample was characterized using XRD, structural analysis, SEM/EDS, and simultaneous thermal analysis. The electrochemical performance of the electrode was estimated in 3M KOH in a standard electrochemical cell for corrosion studies using cyclic voltammetry, impedance spectra, galvanostatic charge/discharge, and long-term cycling stability. The study demonstrated that the SDC exhibits high oxygen mobility and has the ability to release or incorporate oxygen from the gas phase. This process leads to the formation of structural anion vacancies without compromising the structural integrity. The SDC electrode demonstrates a specific capacitance of approximately 500 F/m² and exhibits satisfactory cyclability. Electrochemical treatment in charge–discharge cycles has been shown to result in the formation of a thin strontium-depleted layer on the electrode surface. The observed behavior is believed to be caused by a high concentration of oxygen vacancies, which is consistent with oxygen intercalation into the perovskite structure. The present study suggests that rare earth-doped strontium cobaltite may serve as a prospective precursor for electrode material in supercapacitors.

https://doi.org/10.1016/j.jallcom.2025.185110

Complex investigations of a solid-state reaction process were carried out in bilayer and multilayer thin films of Al/Pt and (Al/Pt)₁₅ by the methods of simultaneous thermal analysis, transmission electron microscopy, in situ electron diffraction, and X-ray diffraction. The solid-state reaction between the aluminum and platinum layers was found to start with the formation of an amorphous a-Al₂Pt phase. The sequence of the phase formation in the solid-state reaction was determined to be the following: Al+Pt→a-Al₂Pt→Al₃Pt₂→Al₂₁Pt₈→Al₄Pt. Thermokinetic modeling of the solid-state reaction was made in the Al/Pt films under study. The “An” type of reaction (n-dimensional formation of grains followed by crystallite growth) was shown to most accurately correspond to the formation of the a-Al₂Pt phase. The formation of the Al₃Pt₂ phase was revealed to occur in two sequential stages: the first stage corresponds to the “Bna” type of reaction (a chain mechanism of grain formation followed by fast crystallite growth), while the second stage belongs to the “R3” type of reaction (three dimensional diffusion along grain boundaries and/or a reaction on grain boundaries which proceeds according to the type of a contracting sphere). With regard to the Al₂₁Pt₈ and Al₄Pt phases, their formation process can be best described by a kinetic model which consists of two parallel reactions. The “An” type of reaction corresponds to the formation of the Al₂₁Pt₈ phase, with the “Cn-Х” type of reaction (a reaction with autocatalysis with grain formation following the chain mechanism) corresponding to the formation of the Al₄Pt phase. Kinetic parameters of the phase formation for a-Al₂Pt, Al₃Pt₂, Al₂₁Pt₈ and Al₄Pt, were determined, with those for Al₂₁Pt₈ and Al₄Pt found for the first time.

https://doi.org/10.1016/j.optcom.2025.132681

In the present work, we report the first experimental observation of Talbot effect caused by a linear periodic arrangement of fork-shaped dislocations. The presence of dislocations imposes phase discontinuities to the optical field given rise to forming an array of optical vortices co-propagating behind the structure. Two types of masks have been considered, with the same or alternating signs of topological charges. Unlike the mask with the same signs of topological charges, a multi-fork grating with alternating signs of dislocations exhibits the Talbot effect. The observed Talbot effect proved by correlation analysis is conditioned by the modality of an array of fork-shaped dislocations under consideration. Theoretical and numerical results are found to be in good correspondence with experimental data. By unveiling the intricate dependencies of optical vortex trajectories on configuration of dislocation arrangement and topological charge distribution therein, this work has advanced the state of the understanding of structured singular optics, paving the way for innovative applications in optical manipulation, communications, and complex light field engineering.

https://doi.org/10.1016/j.jallcom.2025.185110

Complex investigations of a solid-state reaction process were carried out in bilayer and multilayer thin films of Al/Pt and (Al/Pt)₁₅ by the methods of simultaneous thermal analysis, transmission electron microscopy, in situ electron diffraction, and X-ray diffraction. The solid-state reaction between the aluminum and platinum layers was found to start with the formation of an amorphous a-Al₂Pt phase. The sequence of the phase formation in the solid-state reaction was determined to be the following: Al+Pt→a-Al₂Pt→Al₃Pt₂→Al₂₁Pt₈→Al₄Pt. Thermokinetic modeling of the solid-state reaction was made in the Al/Pt films under study. The “An” type of reaction (n-dimensional formation of grains followed by crystallite growth) was shown to most accurately correspond to the formation of the a-Al₂Pt phase. The formation of the Al₃Pt₂ phase was revealed to occur in two sequential stages: the first stage corresponds to the “Bna” type of reaction (a chain mechanism of grain formation followed by fast crystallite growth), while the second stage belongs to the “R3” type of reaction (three dimensional diffusion along grain boundaries and/or a reaction on grain boundaries which proceeds according to the type of a contracting sphere). With regard to the Al₂₁Pt₈ and Al₄Pt phases, their formation process can be best described by a kinetic model which consists of two parallel reactions. The “An” type of reaction corresponds to the formation of the Al₂₁Pt₈ phase, with the “Cn-Х” type of reaction (a reaction with autocatalysis with grain formation following the chain mechanism) corresponding to the formation of the Al₄Pt phase. Kinetic parameters of the phase formation for a-Al₂Pt, Al₃Pt₂, Al₂₁Pt₈ and Al₄Pt, were determined, with those for Al₂₁Pt₈ and Al₄Pt found for the first time.

https://doi.org/10.1016/j.optcom.2025.132681

In the present work, we report the first experimental observation of Talbot effect caused by a linear periodic arrangement of fork-shaped dislocations. The presence of dislocations imposes phase discontinuities to the optical field given rise to forming an array of optical vortices co-propagating behind the structure. Two types of masks have been considered, with the same or alternating signs of topological charges. Unlike the mask with the same signs of topological charges, a multi-fork grating with alternating signs of dislocations exhibits the Talbot effect. The observed Talbot effect proved by correlation analysis is conditioned by the modality of an array of fork-shaped dislocations under consideration. Theoretical and numerical results are found to be in good correspondence with experimental data. By unveiling the intricate dependencies of optical vortex trajectories on configuration of dislocation arrangement and topological charge distribution therein, this work has advanced the state of the understanding of structured singular optics, paving the way for innovative applications in optical manipulation, communications, and complex light field engineering.

DOI: https://doi.org/10.1103/kcm2-2mz4

We investigate the impact of quantum noise on non-Hermitian resonators at an exceptional point. The system's irreversible Markovian dynamics is modeled using the Lindblad master equation, which accounts for the incoherent pump, radiative losses, and external monochromatic field. An exact analytic solution is derived in the form of the characteristic function of the Husimi distribution, enabling the calculation of all quantum mechanical observables associated with the bosonic degrees of freedom. Our analysis reveals that quantum noise strongly influences the system's response when the system exhibits 𝒫⁢𝒯 symmetry. Out of the 𝒫⁢𝒯-symmetric regime, however, the system demonstrates stability within a specific parametric domain, where the effects of quantum noise on the signal-to-noise ratio can be mitigated by increasing the external field.

DOI: https://doi.org/10.1103/xzzp-w7bd

The evolution of the role of lattice vibrations in the formation of the pseudogap state in strongly correlated electron systems has been investigated concerning changes in the electron-phonon coupling parameters and the concentration of doped charge carriers. We apply the polaronic version of the generalized tight-binding method to analyze the band structure of a realistic multiband two-dimensional model that incorporates the electron-lattice contributions of both Holstein and Peierls types. It has been demonstrated that the emergence of polaronic effects begins with the modulation of spectral function intensity. However, within a specific region of the phase diagram, a significant transformation of the electron band structure and pseudogap state occurs. It results from coherent polaron excitations that create a partially flat band near the Fermi level. This process leads to a change in the topology of the Fermi surface and the emergence of corresponding features in the density of states.

https://doi.org/10.1103/22j6-2p89

The electronic structure of the lightly hole-doped triangular-lattice moiré Hubbard model is studied within cluster perturbation theory (CPT) using 13-site clusters for a fixed doping concentration p=1/13 varying the Coulomb parameter U and the hopping phase parameter \phi related to the spin-orbital interaction. We have also developed a rather simple generalized mean-field approximation (GMFA) containing the amplitude of the spin correlations as a free parameter to fit the CPT this http URL evolution of the Fermi surface and the pseudogap with the parameters \phi and U is explained from the viewpoint of the short-range magnetic order. The geometric frustration and the additional model parameter related to the spin-orbital interaction result in a more rich physics of the pseudogap state compared to the case of a more conventional square lattice.

https://doi.org/10.1134/S1062873825713182

Nickel ferrite powders with a particle size of 4 nm were prepared by chemical coprecipitation. The imaginary part �″ of the magnetic susceptibility was measured at room temperature with a broadband ferromagnetic resonance spectrometer in the frequency range from 100 MHz to 10 GHz. The obtained frequency dependences of �″ are described within the framework of an isotropic superparamagnet model taking into account interparticle interactions.

https://doi.org/10.1016/j.jallcom.2025.184900

Near-infrared (NIR) emitting phosphor-converted LEDs (pc-LEDs) have garnered significant interest due to their promising applications in diverse fields utilizing NIR spectroscopy. Fe³⁺ ions, as promising NIR activators, possess the advantages of being nontoxic and cost-effective, making them ideal candidates for NIR emission. In this work, NaAl_11-xO₁₇: xFe³⁺ phosphors were successfully synthesized, exhibiting a broad NIR emission band ranging from 650 to 850 nm, with the peak emission centered at approximately 770 nm. The phosphors demonstrate a high external quantum efficiency (EQE = 54.01 %) and excellent thermal stability. Distinct emission profiles were observed under three different excitation wavelengths, and four luminescent sites were discussed through low-temperature emission spectra. Furthermore, the electroluminescence (EL) spectrum of the fabricated pc-LEDs shows a strong spectral overlap with the absorption band of phytochrome P_fr, highlighting their great potential for plant lighting applications.

https://doi.org/10.1016/j.mtcomm.2025.114184

The energy and electronic characteristics, as well as crystal parameters of the (Cr_1-xMn_x)₂GeC MAX phase with x = 0.00, 0.25, 0.33, 0.50, 0.67, 0.75, and 1.00 were determined using quantum chemical calculations. As the manganese concentration increases, the stability of the compound is expected to decrease. However, the possibility of experimentally realizing a structure with x > 0.25 has been shown. Epitaxial thin (Cr_1-xMn_x)₂GeC MAX films with x up to 0.33 were synthesized by magnetron co-deposition at an increased technological carbon concentration. The samples were studied using electron spectroscopy, high-energy electron diffraction, X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy and reflection spectral ellipsometry. The additional graphitic carbon is identified in the films and is attributed to the peculiarities of the deposition method. An increase in x results in an increase in the parameters of the crystal lattice, a deterioration of the crystalline order, and a decrease in optical conductivity. However, a low manganese concentration (x = 0.25) enhances epitaxy compared to Cr₂GeC. A threefold increase in the thickness of the (Cr_0.75Mn_0.25)₂GeC film results in an increase in the fraction of the secondary (013) structure and a weakening of the primary (00L) structure, though the single-phase nature of the film is preserved.

 https://doi.org/10.1007/s10948-025-07074-8

In a two-band system, both conventional sign-preserving �++ and unconventional sign-changing �± superconducting state may appear at low temperatures. Moreover, they may transform from one to another due to the impurity scattering. To study the details of such a transition here we derive the expression for the Grand thermodynamic potential Ω for a two-band model with nonmagnetic impurities considered in a �-matrix approximation. For the iron-based materials within the multiband Eliashberg theory, we show that the �±→�++ transition in the vicinity of the Born limit is a first order phase transition.

https://doi.org/10.48550/arXiv.2501.17432

Many microscopic models with the interaction between the next-nearest neighbours as a key parameter for cuprate physics have inspired us to study the diagonal superexchange interaction in a CuO layer. Our investigation shows that models with extended hopping provide a correct representation of magnetic interactions only in a hypothetical square CuO layer, where the diagonal superexchange interaction with the next-nearest neighbors always has the AFM nature. The conclusions are based on the symmetry prohibition on FM contribution to the diagonal superexchange between the next-nearest neighbors for a simple square CuO layer rather than for a real CuO layer, where diagonal AFM superexchange may be overestimated. We also discuss the reasons for magnetic frustration effects and high sensitivity of spin nanoinhomogeneity to square symmetry breaking.

 https://doi.org/10.1002/chem.202502070

https://arxiv.org/abs/2504.02452

DOI: https://doi.org/10.1103/PhysRevB.85.125307

DOI: https://doi.org/10.1103/1z7s-wcw6

We consider thermo-optic bistability in resonant excitation of high-quality modes in two-dimensional dielectric resonators. We develop a coupled-mode theory approach which account for the frequency shift due to a temperature dependent dielectric permittivity. The model is applied to rectangular and hexagonal resonators supporting an isolated high-quality resonant mode. The results are verified in comparison with straightforward finite-element simulations. It is shown that the model accurately describes the effect bistabily which occurs under variation of the angle of incidence or the intensity of the incident wave. In particular, it is demonstrated that variation of the incident angle can optimize the coupling between the resonator and the incident waves leading to bistabily with low intensity incident waves . The bistability threshold is shown to be extremely sensitive to the imaginary part of the dielectric permittivity .