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Abstract: This work is devoted to a theoretical description of polarized Møller scattering. Complete one-loop electroweak radiative corrections are calculated in the helicity amplitude approach with allowance for the exact dependence on the muon mass. Numerical results are presented for integrated unpolarized and polarized cross sections as well as angular differential distributions. Calculations are performed using ReneSANCe Monte Carlo generator and MCSANC Monte Carlo integrator. PubDate: 2022-04-26
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Abstract: Realization of soliton-combs regimes in χ(2) microresonators is an important and timely problem. No regular techniques for its solution is known so far. We propose and develop a general method of how to achieve and control numerous stable soliton states possessing spectrally broad combs in the first harmonic (FH) and second harmonic (SH) frequency domains. The method is based on combining special choices of experimentally controlled frequency detunings with a slow adiabatic increase of the pump power starting from near-threshold values. This ensures stability and accessibility of the steady-state regimes. The found new nonlinear solutions are relevant to pumping into SH modes. This allows for the excitation of single- and multi-soliton states of different spatial symmetry – periodic and antiperiodic. PubDate: 2022-04-26
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Abstract: Cobalt-rich Heusler compounds represent a very interesting family of Heusler alloys owing to their performance in spintronics and magnetic devices. The quaternary Heusler, created by swapping of an anti-atom site with an alkali element, improves the performance of physical properties for applications. In this study, the electronic structures and magnetic properties before and after substitution of Co by Li in the Co2NbAl compound were investigated using first-principles computational calculations. Our findings revealed that substitution of Co antisites by Li destroys the half-metallic character of Co2LiNbAl. Analysis of the band structures shows that the parent ternary Heusler compound is ferromagnetic half-metallic with a half-metallic gap (band gap in the minority channel) equal to 0.497 eV. Using the HSE06 approach substituting of Co by Li leads the material to change its behavior and becomes a semiconductor with a gap equal to 1.043 eV. The results of optical and thermoelectric properties such as absorption coefficient, reflectivity or thermo power, and figure of merit are very interesting in the optoelectronic field and encourage researchers to realize photovoltaic cells and thermoelectric generators with higher efficiency. These interesting features suggest that Co2NbAl and LiNbAlCo Heusler compounds are good candidates for applications in spintronics and optoelectronics for commercial semiconductor industry. PubDate: 2022-04-26
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Abstract: Deep inelastic scattering data on F2 structure function accumulated by various collaborations in fixed- target experiments are analyzed in the nonsinglet approximation and within \(\overline {MS} \) and DIS schemes. The study of high statistics deep inelastic scattering data provided by BCDMS, SLAC and NMC collaborations, is carried out by applying a combined analysis. The application of the deep inelastic scheme leads to the resummation of contributions that are important in the region of large x values. It is found that using the deep inelastic scheme does not significantly change the strong coupling constant itself but does strongly change the values of the twist-four corrections. PubDate: 2022-04-11
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Abstract: The notion of the Planckian dissipation is extended to the system of the Caroli-de Gennes-Matricon discrete energy levels in the vortex core of superconductors and fermionic superfluids. In this extension, the Planck dissipation takes place when the relaxation time τ is comparable with the quantum Heisenberg time tH = \(\hbar \) /ΔE, where ΔE is the interlevel distance in the vortex core (the minigap). This type of Planck dissipation has two important physical consequences. First, it determines the regime, when the effect of the axial anomaly becomes important. The anomalous spectral flow of the energy levels along the chiral branch of the Caroli-de Gennes-Matricon states becomes important in the super-Planckian region, i.e. when τ < \(\hbar \) /ΔE. Second, the Planck dissipation separates the laminar flow of the superfluid liquid at τ < \(\hbar \) /ΔE and the vortex turbulence regime at τ > \(\hbar \) /ΔE. PubDate: 2022-04-11
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Abstract: How should modern people evaluate Feynman diagrams' This question has been receiving considerable attention in recent years. While the current answer is far from being complete, one can select several attack directions under development. One of such directions is the differential equations method. We attempt to review some of its features and outline the ideas that could help establish a more general framework. PubDate: 2022-04-11
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Abstract: Measurements of magnetotransport in high quality InN nanowires in presence of conductive atomic-force microscope tip performed at a temperature of T = 4.2 K are presented. We demonstrate evidence of influence of the close to nanowire placed AFM tip at certain ranges of the back gate voltages and the decreasing of the influence in external magnetic field of B ≥ 150 mT. We explain such a behavior by presence of the branched current under the surface of the InN nanowire similar to ones of two-dimensional electrons in heterostructures and graphene samples with point contacts. PubDate: 2022-04-11
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Abstract: In the framework of dynamical mean field theory (DMFT) we analyze Hall effect in doped Mott insulator as a parent cuprate superconductor. We consider the partial filling (hole doping) of the lower Hubbard band and calculate the dependence of the Hall coefficient and Hall number on hole doping, determining the critical concentration for sign change of the Hall coefficient. Significant temperature dependence of the Hall effect is noted. A good agreement is demonstrated with the concentration dependence of the Hall number obtained in experiments in the normal state of YBCO. PubDate: 2022-03-25
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Abstract: A theoretical investigation of the thermal conductivity of lightly Sr- and Zn-doped La2CuO4 high temperature superconductor cuprates has been analysed auspiciously. We used a quantum dynamical technique to develop the symbol of relaxation time and other scattering processes from frequency (energy) line widths in this formulation. The primary focus of this study is the effect of phonon-dopant atom scattering on the thermal conductivity of doped La2CuO4, as well as other dominant scattering mechanisms such as electron-phonon, cubic and quartic anharmonic phonon, cubic and quartic phonon interference, and phonon-magnon, among others. An acceptable level of agreement between theory and experiment has been reached. PubDate: 2022-03-25
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Abstract: We calculate the parallel upper critical magnetic field H (0) for an in-plane isotropic quasi-two-dimensional (Q2D) chiral triplet superconductor at zero temperature, T = 0. In particular, the ratio H (0)/( d \(H_{{ }}^{{GL}}\) /d \(T{{{\text{ }}}_{{T = {{T}_{c}}}}}\) Tc) = 0.815 is defined, where d \(H_{{ }}^{{GL}}\) /d \(T{{{\text{ }}}_{{T = {{T}_{c}}}}}\) is the so-called Ginzburg–Landau slope of the upper critical magnetic field, Tc is a superconducting transition temperature at H = 0. We show that the theoretically obtained above mentioned value strongly contradicts to the experimentally measured ones in a candidate for a chiral triplet superconductivity Sr2RuO4, which provides one more argument against the chiral triplet scenario of superconductivity in this compound. Our results may be useful for establishing chiral triplet superconductivity in other Q2D candidates for this phenomenon. PubDate: 2022-03-15
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Abstract: Recently new topological phase of superfluid 3He has been discovered – the β phase, which is obtained by strong polarization of the nematic polar phase. We consider half-quantum vortices, which are formed in rotating cryostat, and discuss the evolution of the vortex lattice in the process of the transition from the polar phase to the β-phase via the spin-polarized polar phase. PubDate: 2022-03-03 DOI: 10.1134/S0021364022100071
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Abstract: Three-dimensional van der Waals ferromagnet Fe3GeTe2 (FGT) is regarded as a candidate for the magnetic topological nodal line semimetal. We investigate lateral electron transport between two 3 μm spaced superconducting In leads beneath a thick three-dimensional FGT exfoliated flake. At low 30 mK temperature, we observe Josephson supercurrent that exhibits unusual critical current Ic suppression by the magnetic field B. The overall Ic(B) pattern is asymmetric in respect of the B sign. We demonstrate, that the asymmetry is defined by the magnetic field sweep direction, so the Ic(B) pattern is strictly reversed (as B to –B inversion) for the opposite sweeps. We also observe an interplay between maximum and minimum in Ic(B) in normal magnetic fields, while there are fast aperiodic Ic(B) fluctuations for the in-plane ones. These effects can not be expected for homogeneous superconductor-ferromagnet-superconductor junctions, while they are known for Josephson spin valves. The mostly possible scenario for Josephson spin valve realization in FGT is the misalignment of spin polarizations of the Fermi arc surface states and ferromagnetic FGT bulk, but we also discuss possible influence of spin-dependent transport between magnetic domains. PubDate: 2022-03-03 DOI: 10.1134/S0021364022100101
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Abstract: In this paper we present results of our search for extended high-energy emission around M87 – the central galaxy in the Virgo cluster. The M87 galaxy harbors extremely heavy supermassive black hole, MBH > 4 × 109 \({{M}_{ \odot }}\) and for the last 100 Myr experiences a period of increased activity that resulted in formation of extended lobes, which are prominent radio- and X-ray sources. We perform a search in 13 years of the Fermi-LAT data in three energy bins: 0.1–1, 1–10, and 10–100 GeV. No significant detection of extended emission was achieved in any bin, with weak indication of a signal (~2.5σ) in the last bin (10–100 GeV). We used γ-ray observations to put limits on cosmic rays population in the lobes, constraining their fraction X in comparison to the thermal energy of the hot gas. Depending on the value of spectral index, for electrons Xe < (0.1–0.2) and protons were constrained at Xp < (0.2–0.5) level. We confirm that cosmic rays is a subdominant component of the lobes, which are dominated by thermal gas. PubDate: 2022-03-03 DOI: 10.1134/S0021364022100137
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Abstract: Here, we experimentally and theoretically demonstrate a laser-induced change in local color based on the reshaping of gold-silicon asymmetric nanostructures. The evolution of scattering properties enabled by laser reshaping shows the potential of hybrid metal-dielectric nanostructures for color printing applications. The reshaping process can tune the resonance of the nanostructure in the wavelength range between 500 and 800 nm resulting in different colors of illuminated nanostructures. Moreover, the modeling of the scattering diagram of hybrid nanoparticles before and after fs-laser reshaping shows that color tuning is simultaneously accompanied by substantial reconfiguration of the distribution pattern for both peaks in the scattering spectrum. PubDate: 2022-02-14 DOI: 10.1134/S0021364022040014
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Abstract: A thermodynamically consistent phase-field model of locally nonequilibrium solidification of concentrated two-phase binary solutions is proposed. The model is based on the division of the impurity concentration field into independent concentration fields formally defined in the entire available space for each of the phases. The impurity dynamic equations follow from the division of the complete impurity conservation law into separate phases. The phase-field equation and flow expressions are derived from the general principles of nonequilibrium thermodynamics. A feature of the derived equations is the impurity capture by the growing phase when the interface moves. Diffusion flow is divided into processes and phases. The resulting model has been tested using numerical simulation of a one-dimensional problem of directional solidification of a Si–As solution. PubDate: 2022-02-01
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Abstract: Magnetic topological insulators (TIs) are narrow-gap semiconductor materials combining a nontrivial band structure and the magnetic order. Unlike their nonmagnetic analogs, magnetic TIs can have a band gap in the electronic structure of surface states, which allows a number of exotic phenomena such as the quantum anomalous Hall effect and chiral Majorana fermions, which can be applied in spintronics. Up to now, magnetic TIs were fabricated only by doping with 3d transition metals (Cr, Co, V, Fe, Mn). However, such an approach provides these materials with strongly inhomogeneous magnetic and electronic properties, which allow the observation of the mentioned effects only at very low temperatures. An intrinsic magnetic TI, which is a well-ordered stoichiometric magnetic compound, can be an ideal solution to these problems. In this review, an experimental study of the electronic and magnetic properties of the first representative MnBi2Te4 of the intrinsic magnetic TI, as well as the (MnBi2Te4)(Bi2Te3)m, m ≥ 1, family of such TIs constructed from a sequence of MnBi2Te4 magnetic blocks separated by m Bi2Te3 nonmagnetic blocks, is presented. The effect of magnetism on the electronic structure is the strongest in MnBi2Te4 and decreases with increasing m. In particular, MnBi2Te4 has antiferromagnetically ordered Mn layers in neighboring blocks and a magnetic transition temperature (Néel temperature) of about 24.5 K. The antiferromagnetic order is also observed in compounds with m = 1 and 2, but the ordering temperatures are much lower, 13 and 11 K, respectively. At larger m values, MnBi2Te4 magnetic blocks hardly interact with each other and are in essence two-dimensional magnets. The electronic structure of topological surface states for this family is characterized by a single Dirac cone whose form and properties depend on m and on magnetic/nonmagnetic termination at m ≥ 1. In the case of magnetic termination of the surface, the gap can be opened at the Dirac point. It is maximal for MnBi2Te4 and is expected to be 80–90 meV. However, the possibility of its variation in the range from almost 0 to 70 meV for various samples is experimentally demonstrated. To determine the reasons for such deviations, density functional theory calculations are performed. PubDate: 2022-02-01
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Abstract: A modification of the low-field ferromagnetic resonance (FMR) spectra of an easy-plane BiY2Fe4.4Sc0.6O12 film under irradiation with linearly polarized light with a wavelength of 680 nm at room temperature is experimentally detected. It is shown that the photoinduced change in the magnetic anisotropy is not related to thermal effects and it leads to a shift of the FMR frequency. A photoinduced decrease in the magnetoelastic coupling is indicated by a decrease in the depth of dips in the FMR spectra at frequencies corresponding to the resonance of transverse modes of elastic vibrations over the thickness of the epitaxial structure. The observed effects are due to a change in the populations of the energy levels of photoactive centers in the impurity magnet. It has been shown that the contribution to the photoinduced shift of the FMR frequency that depends on the direction of light polarization is an order of magnitude smaller than the main contribution that does not depend on the direction of polarization. The dependence of the FMR frequency on the direction of the electric field vector of the light wave is due to the nonlinear interaction of light and magnetization, which is described by the fourth-rank material tensor. PubDate: 2022-02-01
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Abstract: Features of the simultaneous action of longitudinal and transverse ultrasonic vibrations in the quartz crystal on the parameters of reflected X-rays are studied. It is shown that this action results both in the X-ray acoustic conversion effect, which is an increase in the intensity of radiation diffracted by the crystal at the excitation of transverse vibrations with linear polarization, and in the broadening of the rocking curve, which is due to the formation of a standing wave in the crystal at longitudinal vibrations. It is demonstrated for the first time that several key parameters of X-rays can be simultaneously controlled using a single crystal. Transverse vibrations make it possible to vary the intensity of diffracted radiation, and longitudinal vibrations allow controllable angular rearrangement of the X-ray beam diffracted by the crystal. PubDate: 2022-02-01
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Abstract: A FeCr2O4 single crystal with the spinel structure is grown by the zone melting method with optical heating. The critical temperatures of establishing the orbital ordering TOO = 138 K, the formation of the collinear ferrimagnetic state TN = 65 K, and the formation of the spiral modulation of the magnetic structure Ts = 38 K are determined from the temperature dependences of the heat capacity and magnetic susceptibility. An anomaly of the susceptibility at T ~ 21 K, below which the hysteresis curves become butterfly-like is probably caused by a change in the magnetic anisotropy. It is established that the magnetic resonance spectrum in the microwave X-band (~9.4 GHz) at T = 30 K changes under the reversal of the direction of the external magnetic field (nonreciprocity phenomenon). Magnetic and induced electric dipole transitions are considered theoretically. The detected nonreciprocity is explained by the interference of these transitions. PubDate: 2022-02-01
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Abstract: Detailed measurements of the Hall effect in the Ho0.8Lu0.2B12 antiferromagnetic compound (Néel temperature TN = 5.75 K) in magnetic fields up to 80 kOe oriented in the (110) plane at temperatures of 1.9–6.6 K are performed. It is established with the contribution separation procedure that the anisotropic positive contribution, which is responsible for the double inversion of the sign of the Hall resistance, dominates in the antiferromagnetic state of Ho0.8Lu0.2B12 in fields of 30–50 kOe. A sharp decrease in the amplitude of the isotropic negative contribution at the transition to the antiferromagnetic phase is found. The nature of the detected anomalies in the antiferromagnetic metal with dynamic charge stripes and spin-wave component of the magnetic structure is discussed. PubDate: 2022-02-01
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