


卷 117, 编号 1-2 (1) (2023)
Articles
Dynamical Correlations in the Ground State: Transitions between One-Phonon Nuclear States
摘要
The probabilities of the E1 transition between the first
and @ excited levels in nuclei with pairing have been calculated within the self-consistent many-body nuclear theory and Green’s function method. Calculations for a long chain of even–even tin isotopes have been performed for the first time. The known Fayans energy density functional has been used to calculate the characteristics of phonons and E1 transitions between excited states. A good description has been achieved for existing experimental data for the reduced probabilities of E1 transitions between the first one-phonon states for the 116–124Sn isotopes but not for the 112Sn and 114Sn isotopes. Possible reasons for this discrepancy have been discussed; the most probable reason is the deformation in the ground or excited states. It has been shown that new dynamical three-quasiparticle correlations in the ground state should be taken into account to explain the experimental data for 116–124Sn.



Unipolar and Subcycle Extremely Short Pulses: Recent Results and Prospects (Brief Review)
摘要
In recent years, progress has been made in obtaining extremely short electromagnetic pulses up to single-cycle and unipolar half-cycle pulses. For pulses with such a dependence of the electric field strength on time, the behavior and properties of such radiation and its interaction with matter acquires a number of new features. For extremely short unipolar pulses an important role in the interaction with matter is played by the electric pulse area (the integral of the electric field strength over time at a given point in space). The review presents the latest theoretical and experimental results in the field of obtaining and interaction of extremely short pulses with extended resonant media and individual microobjects (atoms, molecules, nanostructures). The results of new publications are discussed, in which phenomena are predicted that arise during the coherent propagation of extremely short pulses in resonant media—self-compression and self-stopping of a pulse in a homogeneous medium. Particular attention is paid to the effect of ultrashort pulses on microobjects from the point of view of the recently introduced concept of “interference” of pulse areas (electrical area and envelope area). The research results presented in the review relate to a new direction in modern optics that has emerged recently—“Optics of unipolar and subcycle light,” which is becoming an actively developing area of modern physics.



Theoretical Foundations of Quantum Spectral-Domain Optical Coherence Tomography with Frequency Scanning
摘要
A quantum spectral-domain optical coherence tomography technique based on the control of the joint spectral amplitude of a biphoton has been developed. An analytical expression for a quantum spectral-domain optical coherence tomography signal has been obtained in the case of a Gaussian joint spectral amplitude. The effect of the shape of the joint spectral amplitude of the biphoton on the resulting interference signal has been analyzed. The possibility of improving the quality of the interference signal by controlling the parameters of the joint spectral amplitude has been considered. It has been shown theoretically that the proposed approach provides a higher longitudinal spatial resolution than other optical coherence tomography techniques.



Two-Photon Laser Lithography of Functional Microstructures of Integrated Photonics: Waveguides, Microcavities, and Prism Input/Output Adapters of Optical Radiation
摘要
The development and optimization of methods for creating functional elements of micron and sub-micron sizes for photonic integrated circuits is one of the main tasks of nanophotonics. Two-photon laser lithography is actively developing now to form three-dimensional structures with subwave resolution. Results of this development are reported and it is shown that the use of optimized lithography schemes, the spatial filtering of laser beam used, and the introduction of laser dyes into polymer lead to the formation of optically homogeneous high-quality bulk microstructures with characteristic features down to 300 nm with necessary functional properties. The capabilities of optimized two-photon laser lithography are demonstrated by examples of ring microcavities and optical waveguides with prism input/output adapters located above a substrate. Optical losses upon the coupling of 405-nm radiation into a waveguide using a printed prism adapter was no more than 1.25 dB.



Observation of Magnetic-Field-Induced Electric Polarization in Terbium Orthoferrite
摘要
In TbFeO3 orthoferrite at temperatures below the antiferromagnetic ordering temperature for the terbium subsystem (∼3.2 K), the electric polarization Pa(Hb) induced by a magnetic field Hb along the a axis is found. Such polarization is accompanied by anomalies related to metamagnetic (for Tb) and spin-reorientation (for Fe) transitions. At low magnetic fields |H| < Hcr1 ∼ 5 kOe, the Pa(Hb) dependence exhibits a strong hysteresis and has a “butterfly” shape, while in intermediate-field magnetic configurations, |Hcr1| < |H| < |Hcr2| ~ 18 kOe, the sign of the polarization is determined by the sign of an applied electric field, and the Pa(Hb) dependence turns out to be nonmonotonic. A qualitative explanation of the observed effects is given in the framework of a symmetry analysis of the allowed magnetoelectric interactions in the field-induced magnetic structures.



Interference Transport in a Two-Dimensional Topological Insulator in a CdHgTe Quantum Well
摘要
Interference transport in mesoscopic samples of a two-dimensional topological insulator in CdHgTe quantum wells is studied for the first time. It is established that quasi-ballistic edge transport in such an insulator exists at lengths up to 10 µm. In this transport regime, almost periodic Aharonov–Bohm oscillations caused by the formation of closed loops with a characteristic size of about 200 nm by edge states are found. The phase coherence length in the two-dimensional topological insulator is determined for the first time from the measured temperature dependence of their amplitude.



Hubbard bands, Mott transition and decon nement in strongly correlated systems



Magnetic State of Layered Cobalt Chalcogenides Co7Se8 and Co7Te8
摘要
The structural and magnetic properties of the Co7Te8 layered compound have been studied for the first time using X-ray diffraction, measurements of the magnetic susceptibility, and nuclear magnetic resonance spectroscopy on 59Co nuclei. The nuclear magnetic resonance study of Co7Se8 selenide with the same structural type (NiAs) as Co7Te8 has also been performed for the first time. In contrast to Co7Se8, the ordering of vacancies and Co atoms in cation layers is absent in the Co7Te8 compound, and its crystal structure is more planar and is characterized by a significantly smaller ratio c0/a0 compared to Co7Se8 (a0 and c0 are the basic lattice parameters of NiAs). The components of the magnetic shift and electric field gradient tensors at the location of Co nuclei have been determined. A significant local charge and spin inhomogeneity of the co-mpounds has been revealed. The hyperfine coupling constant in Co ions has been estimated from the te-mperature dependences of the shift and susceptibility in Co7Te8. An anisotropic increase in the interatomic distances does not increase the localization of
electrons and does not lead to the appearance of magnetic moments on Co atoms in Co7Te8. This compound remains a Pauli paramagnet down to the lowest tempe-ratures.



Electronic Structure of InCo2As2 and KInCo4As4: LDA + DMFT
摘要
A comparative analysis of the electronic structure obtained in the DFT/LDA and LDA + DMFT approaches of the possible isostructural analogues of iron superconductors InCo2As2 and KInCo4As4 with the electronic structure of the parent high-temperature superconductor system BaFe2As2 is carried out. It is established that in spite of the rather large value of the electron-electron correlations (local Coulomb interaction on the Co-@ shell @ eV, the Hund exchange interaction @ eV), in the considered systems a relatively small quasiparticle mass renormalization 1.2–1.35 at the Fermi level is observed. The correlation effects lead to the remarkable shift and compression of the spectrum below –0.8 eV. The band structure of InCo2As2 near the Fermi level is qualitatively similar to the previously studied BaCo2As2, and differs significantly from the band structure of BaFe2As2. In the KInCo4As4 system, the bands near the Fermi level resemble the band structure of BaFe2As2, and the Fermi surfaces have a similar topology. This indirectly points to the possibility of superconductivity in KInCo4As4. Also according to the results of LDA + DMFT calculations it is seen that with a rather small hole or electron doping in the KInCo4As4 system will experience topological Lifshitz transitions. We believe that the synthesis of the InCo2As2 and KInCo4As4 compounds considered in this paper is important for the study of superconductivity in this class of materials.



Unconventional Fractional Quantum Hall States in a Wide Quantum Well
摘要
A bilayer electron system that is formed in a 60-nm-wide GaAs quantum well and has a large difference of the electron densities in the layers has been studied. It has been found that, when a magnetic field is tilted from the normal to the plane of the system, integer quantum Hall effect states at the filling factors of Landau levels of 1 and 2 disappear; instead, fractional quantum Hall effect states in the interval between these filling factors appear at the filling factors νF = 4/3, 10/7, and 6/5 with odd denominators and at the filling factor νF = 5/4. Several different states can be observed under the variation of the magnetic field. The detected fractional quantum Hall effect states are interpreted as combined states with the same filling factor 1 in the layer with the higher density and with the filling factors νF – 1 in the layer with the lower density. These states are formed because of the redistribution of electrons between the layers, which occurs under the variation of the magnetic field. The appearance of the state with the filling factor νF = 5/4 with the even denominator is presumably attributed to the dominance of the interlayer electron–electron interaction over the intralayer one for electrons in the layer with the lower density.



Quantum Algorithm for the Invariant Estimate of the Closeness of Classical Ciphers to the One-Time Pad
摘要
An invariant measure of the closeness of a block cipher to the perfect (ideal) cipher of the one-time pad has been proposed. The measure is the same for any implementation of the one-time pad. A quantum algorithm based on the determination of the eigenvalue (phase) of the quantum state has been proposed to estimate the closeness of the block cipher to ideal in terms of the proposed measure with high probability and accuracy.



Interconnected evolution of epidemic and public vaccination opinion
摘要
A new model of interconnected coevolving SIRS epidemic and public vaccination opinion pattern is presented. The underlying two-layer network contains strata corresponding to physical interactions in real space and social communications. The layer corresponding to physical interactions is constructed based on data on a real network representing communications between high school students. The evolution of people vaccination attitude is described using an Ising-type model. The model describes a non-trivial dependence of resulting epidemic dynamics on (1) noise amplitude, (2) initial opinion pattern and (3) influence of external information.



Systematic Effects in the Measurement of the Lifetime of the Neutron in Magnetic Traps of Ultracold Neutrons
摘要
Possible systematic effects in experimental measurements of the lifetime of the neutron using magneto-gravitational traps to store ultracold neutrons have been discussed. Methods for the online detection of possible losses, including depolarization losses and a small heating of neutrons stored in a trap, have been proposed.



Long-range Multiparticle Interactions Induced by Neutrino Exchange in Neutron Star Matter
摘要
Forces with a large radius of interaction can have a significant impact on the equation of state of matter. Low-mass neutrinos generate a long-range potential due to the exchange of neutrino pairs. We discuss a possible relationship between the neutrino masses, which determine the interaction radius of the neutrino-pair exchange potential, and the equation of state of neutron matter. Contrary to previous statements, the thermodynamic potential, when decomposed into the number of neutrino interactions, vanishes in any decomposition order, except for the interaction of two neutrons. In the one-loop approximation, long-range multiparticle neutrino interactions are stable in the infrared region for all neutrino masses and do not affect the equation of state of neutron matter or the stability of neutron stars.



Quasistationary Polariton States in Mesocavities
摘要
When the strength of light–matter interaction (the Rabi splitting) in mesocavities is comparable to the energy spacing between the cavity modes, an exciton mode is coupled simultaneously to a number of optical modes. It has recently been demonstrated that a nonmonotonic dependence of the population of polariton states in mesocavities on the pump intensity is possible. Here, it is shown that an additional quasistationary state may appear in the hysteresis region and the time spent by the system in this state depends on the pump intensity.



Determination of the Most Important Parameters of a Metal Irradiated by an Ultrashort Laser Pulse
摘要
Ultrashort laser pulses with a duration from several to about a thousand optical cycles have significant importance in modern science and engineering. Such a pulse transfers a metal to an excited two-temperature state with hot electrons where the temperature of the electron subsystem Te is much higher than the temperature of the ion subsystem Ti. The thermal conductivity in such systems differs from well-known reference values. The thermal conductivity κ and the energy exchange rate between the electron and ion subsystems α are the key parameters of the two-temperature model, which are still poorly studied, although studies of these parameters, particularly α, are numerous. New theoretical and experimental results that make it possible to determine the parameters κ and α for gold have been reported in this work



Optical Properties of Silicon Nanowires Obtained by Metal-Assisted Chemical Etching Using Gold Nanoparticles
摘要
Owing to their unique structural and physical properties, silicon nanowires are a promising material for electronics, photovoltaics, photonics, sensors, and biomedicine. Despite the many methods available for the synthesis of silicon nanowires, metal-assisted chemical etching is currently one of the most promising for their cost-effective production. In most works, silver nanoparticles are used as a catalyst for the chemical reaction of crystalline silicon etching. However, the use of gold nanoparticles in metal-assisted chemical etching can significantly affect the morphology and optical characteristics of the prepared samples. In this work, silicon nanowires are synthesized by metal-assisted chemical etching of crystalline silicon using gold nanoparticles. According to high-resolution scanning and transmission electron microscopy, the resulting nanowires have a diameter of about 100 nm and consist of a crystalline core about 50 nm in diameter coated with a SiO2 shell about 25 nm thick with silicon nanocrystals at the interface. The porosity of the silicon nanowire arrays, which has been estimated from their specular reflection spectra and has been calculated using the Bruggeman effective medium model, is 70%. At the same time, the samples exhibit an extremely low (3–7%) total reflection in the spectral region of 250–1000 nm and an increase in the intensities of interband photoluminescence and Raman scattering compared to the initial crystalline silicon substrate, caused by the light localization effect. In addition, the photoluminescence of nanowires has been detected in the range of 500–1000 nm with a maximum at 700 nm, which is explained by the radiative recombination of excitons in silicon nanocrystals with a size of 3–5 nm.



Magnetic Field Effect on the Formation of Ultracold Plasma
摘要
The molecular dynamics method is used to simulate the formation of ultracold plasma under continuous ionizing irradiation in a quadrupole magnetic field with the gradient of the magnetic field along the axis of symmetry equal to 0, 30, 150, and 500 G/cm. An increase in the magnetic field promotes an increase in the plasma density owing to the trapping of some part of fast electrons by the quadrupole magnetic field.



Pair Correlation Function of Vorticity in a Coherent Vortex
摘要
We study the correlations of vorticity fluctuations inside a coherent vortex resulting from the inverse energy cascade in two-dimensional turbulence. The presence of a coherent flow, which is a differential rotation, suppresses small-scale fluctuations of the flow, which are created by an external force, and lead to the fact that these fluctuations can be considered as non-interacting and, therefore, examined in a linear approximation. We calculate the pair correlation function of vorticity and demonstrate that it has a power-law behavior both in space and in time. The obtained results allow us to start a systematic study of the effects associated with the nonlinear interaction of fluctuations, which play an essential role on the periphery of a coherent vortex. Our results are also applicable to the statistics of a passive scalar in a strong shear flow.



Electronic and Magnetic Properties of the ε-Fe Phase at High Pressures up to 241 GPa in the Temperature Range of 4–300 K
摘要
The magnetic and electronic states of iron in the hexagonal close-packed ε-Fe phase have been studied by synchrotron Mössbauer spectroscopy on Fe-57 nuclei (nuclear forward scattering method) at pressures of @ GPa in the temperature range of 4–300 K in external magnetic fields up to 5 T. It has been found that Fe atoms are in a nonmagnetic state in the entire studied P–T region. Theoretically implied magnetic instability and quantum spin fluctuations, which can be stabilized by magnetic perturbation (e.g., external magnetic field), have not been confirmed by our measurements of nuclear forward scattering spectra in an external magnetic field. It has been established that the isomer shift IS(P) has a nonlinear pressure dependence and reaches a colossal value of about –0.8 mm/s at a maximum pressure of 241 GPa, indicating a very high electron density on the Fe nucleus. A sharp change in the electron density on the Fe nucleus at temperatures of 100–200 K indicates a phase transition with a change in the electronic structure, which can be due to an abrupt increase in the conductivity or even to the appearance of superconductivity.



Adsorption of Na monolayer on graphene covered Pt(111) substrate



Electronic Spectrum Features under the Transition from Axion Insulator Phase to Quantum Anomalous Hall Effect Phase in an Intrinsic Antiferromagnetic Topological Insulator Thin Film
摘要
In this paper, we investigate the electron topological states in a thin film of intrinsic antiferromagnetic topological insulator, focusing on their relationship with the magnetic texture. We consider a model for the film with an even number of septuple-layer blocks, which is subject to transition from the phase of an axion insulator to the phase of quantized Hall conductivity under an external magnetic field. In the continuum approach, we model an effective two-dimensional Hamiltonian of the thin film of a topological insulator with non-collinear magnetization, on the basis of which we obtain the energy spectrum and the Berry curvature. The analysis of topological indices makes it possible to construct a topological phase diagram depending on the parameters of the system and the degree of non-collinearity. For topologically different regions of the diagram, we describe the edge electronic states on the side face of the film. In addition, we investigate the spectrum of one-dimensional states on the domain wall separating domains with the opposite canting angle. We also discuss the results obtained and the experimental situation in thin films of the MnBi2Te4 compound.



Charge Density and Mobility of Charge Density Waves in the Quasi-One-Dimensional Conductor NbS3
摘要
Three charge density waves (CDWs), two of which are formed above room temperature, are observed in the NbS3 monoclinic phase (NbS3-II). The charge density and mobility in the high-field limit have been determined for each of three CDWs in this work using the synchronization effect of CDWs in high-frequency fields. It has been found that the mobility of each CDW in this limit is approximately equal to the normal-state mobility of quasiparticles condensed in it. Furthermore, correlation has been observed between the temperature dependences of mobilities of CDWs and quasiparticles. The results of this work refresh problems of a mechanism of the limit conductivity of CDWs and of the distribution of CDWs between atomic chains in the unit cell.



Gyrotropic Oscillations of Magnetic Vortices in Two Interacting Ferromagnetic Disks
摘要
The gyrotropic motion of vortex magnetization distributions in two coupled ferromagnetic disks has been experimentally studied and numerically simulated. The dependence of the resonant frequency of the collective gyrotropic oscillation mode of vortices on the distance between the centers of disks has been studied by magnetic resonance force spectroscopy. The energy of the interaction of magnetic vortices as a function of the distance between disks has been estimated from this dependence using solutions of the Thiele equation.



Logarithmic Relaxation of the Nonequilibrium State of the Charge Density Wave in TbTe3 and HoTe3 Compounds
摘要
The measurements of electronic transport including the dynamic properties of the charge density wave (CDW) in the quasi-two-dimensional compound HoTe3 have been performed. The effects of the slow relaxation of the nonequilibrium state of the CDW during isothermal exposure in the zero current mode, previously observed in TbTe3, have been discovered and studied. A significant increase in the exposure time made it possible to clearly demonstrate that the relaxation is logarithmic. Relaxation features were studied in different temperature and time ranges. The data obtained indicate the glassy behavior of the CDW pinning centers in rare-earth tritellurides.


