JETP Letters最新文献

We calculate the medium modification factor ({{I}_{{pA}}}) for 5.02 TeV (p) + Pb collisions. We use the Monte Carlo Glauber model to determine the parameters of the quark–gluon plasma fireball in (pA) jet events. Our calculations show that the jet quenching effect for ({{I}_{{pA}}}) turns out to be rather small. We have found that the theoretical ({{I}_{{pA}}}) as a function of the underlying event charged multiplicity density, within errors, agrees with data from ALICE [1] for 5.02 TeV (p) + Pb collisions. However, the experimental errors are too large to draw a firm conclusion on the possible presence of jet quenching.

Motivated by the considerable importance of material properties in modern condensed matter physics research, and using techniques of the ({{N}_{e}})-electron systems in terms of the electron density ({{n}_{{sigma e}}}left( r right)) needed to obtain the ground-state energy ({{E}_{{e0}}}) in density functional theory scenarios, we approach the exchange-correlation energy ({{E}_{{xc}}}left[ {{{n}_{{sigma e}}}(r)} right]) by considering the interelectronic position corrections (Delta r_{x}^{{ uparrow uparrow , uparrow downarrow }} = ) ({{lambda }_{x}}left| {delta {{r}^{{ uparrow uparrow }}} - delta {{r}^{{ uparrow downarrow }}}} right|) and (Delta r_{c}^{{{{e}_{i}}{{e}_{{j ne i}}}}} = ) ({{lambda }_{c}}{{left| {r - r{kern 1pt} '{kern 1pt} } right|}^{{ - {{{left( {{{N}_{e}} - 1} right)}}^{{ - 1}}}}}}) corresponding to the spin and the Coulomb correlation effects, respectively, through the electron–electron potential energy. Exploiting such corrections, we get approximate expressions for the exchange ({{E}_{x}}left[ {{{n}_{{sigma e}}}} right]) and the correlation ({{E}_{c}}left[ {{{n}_{{sigma e}}}} right]) functional energies which could be interpreted in terms of magnetic and electric dipole potential energies associated with the charge density ({{n}_{{sigma e}}}left( r right)) described by inverse-square potential behaviors. Based on these arguments, we expect that such obtained exchange-correlation functional energy could be considered in the local density approximation functional as an extension to frame such interelectronic effects.

Experiments on the dynamic isentropic compression of solid CO₂ samples by the megabar pressure induced by the superstrong magnetic field of an explosive magnetic generator have been performed with the X-ray diffraction detection of the state of the compressed samples. The generator operation is based on the fast compression of the initial magnetic flux in the cavity of the generator by a conducting cylindrical liner accelerated by the products of the explosion of a cylindrical explosive charge. Two points at pressures of 349 and 459 GPa on the compressibility diagram of CO₂ have been determined in the experiments, where the degree of compression ρ/ρ₀ of CO₂ has reached currently highest values of 3.90 and 4.02, respectively. Comparison has shown that theoretically calculated equations of states for crystal phases of CO₂ almost completely reproduce the experimental results, which confirms a high accuracy of theoretical predictions and the identity of the experimental and theoretical equations of states of CO₂ modifications stable at high pressures.

There are a few materials where single-photon emitters, which are vital elements of quantum communications, can be created and function at room temperature. One of these materials is hexagonal boron nitride. In this study, mechanically assembled homostructures made of two boron nitride sheets are investigated. At the interface between these sheets, microbubbles are formed by adsorbed residues of water molecules and carbon compounds. After high-temperature annealing of the samples, stable room-temperature emitters of single photons in the visible and near infrared bands are formed in the areas of these microbubbles. The observed phenomenon opens the way to the controlled creation of stable emitters using the assembly of homostructures.

Using incoherent multiple Andreev reflection effect spectroscopy, we have studied the multiple-gap superconducting state of underdoped and overdoped Na(Fe, Co)As single crystals. We directly determined the magnitudes of the microscopic superconducting order parameters, their temperature dependences, and characteristic ratios (2Delta (0){text{/}}{{k}_{B}}{{T}_{c}}). The obtained large data statistics unambiguously proves a significant decrease in the degree of the large superconducting gap possible anisotropy in the overdoped compositions away from the antiferromagnetic and nematic regions of the doping phase diagram.

The density of shock-compressed liquid krypton ρ ≈ 9 g/cm³ and the temperature T ≈ 55 000 K on the main Hugoniot adiabat in the pressure range of Р ≈ 140–255 GPa have been measured with hemispherical shock wave generators. Using spherical devices, gaseous krypton has been compressed to the density ρ ≈ 20 g/cm³ by the pressure Р ≈ 2700 GPa at the temperature T ≈ 120 000 K. The experiment has been carried out at the X-ray diffraction complex RGK-B-L (Russian Federal Nuclear Center All-Russian Scientific Research Institute of Experimental Physics) consisting of BIM 234.3000 betatrons with a boundary energy of 60 MeV used in the multipulse bremsstrahlung generation regime with a multichannel optoelectronic detection system for X-ray images. The designs of the experimental devices have been described, and the thermodynamic parameters of the krypton plasma reached in these devices have been estimated. The obtained data have been analyzed and compared to previously reported data. The compression of krypton to the density ρ ≈ 20 g/cm³ by the pressure Р ≈ 2700 GPa is currently a record achievement.

The field dependence of the magnetization along the hard axes in a four-sublattice ferromagnet PbMnBO₄ is calculated by the numerical minimization of the ground state energy in the approximation of classical magnetic moments. The parameters of anisotropic interactions—the second-order single-ion anisotropy constants, the magnitude and direction of the antisymmetric exchange vector, and the symmetric anisotropic exchange tensor—are obtained by a comparison with experimental magnetization curves. The direction of the Dzyaloshinskii–Moriya interaction vector is close to the orthorhombic c axis. The symmetric exchange tensor has an almost uniaxial form with the easy axis perpendicular to the antisymmetric exchange vector. Changes in the energy of each anisotropic interaction during magnetization reorientation are calculated.

A phenomenological model of a “running axial mass” (MArun) was previously proposed to calculate cross sections for the quasielastic scattering of neutrinos and antineutrinos on nuclei. It can be easily implemented in neutrino generators and has only two free parameters, which are obtained from the global fit to the experimental data on the total and differential cross sections for the quasielastic scattering of (anti)neutrinos on various nuclear targets. In this work, the NOvA near detector data on the total and differential cross sections for the scattering of muon neutrinos, are compared to the simulation performed using the GENIE neutrino Monte Carlo generator (v.3.4.0), which optionally allows for using the MArun model.

The structural analogue of iron-based superconductors the BaMn₂P₂ and BaMn₂As₂ compounds under hydrostatic pressure upto 140 GPa were studied within the framework of DFT + U. The transition from an antiferromagnetic insulator to an antiferromagnetic metal is observed under pressure of 6.4 GPa for BaMn₂P₂ and 8.3 GPa for BaMn₂As₂. This second order phase transition to the AFM metallic state provides an appropriate normal state for possible superconductivity in these materials. Moreover, further increase in pressure leads to a series of first order magnetostructural phase transitions between different antiferromagnetic phases, then to a ferromagnetic metal and finally to a nonmagnetic metal. In case of doping, these compounds could potentially be superconductors under pressure (above 6–8 GPa) with critical temperature growing under pressure.

A phase transition accompanied by the appearance of a spike in the longitudinal resistance of a two-dimensional electron system has been studied using the electron spin resonance near the filling factor ν = 3 in the ZnO/MgZnO heterojunction. This transition occurs when the tilt angle θ of the magnetic field is increased to some critical value θ_c. An analysis of the spin resonance amplitude has made it possible to demonstrate the spin nature of this phenomenon. For example, the ground state of the system on both sides of the transition has a nonzero spin polarization, which changes by several times when the phase of the system is changed. Strong spin resonance is observed both at θ < θ_c and at θ > θ_c. Surprisingly, the spin resonance at the critical angle θ_c has been detected in only one phase, which lies in the region of magnetic fields below the critical field B_c corresponding to the spike position in the longitudinal resistance. An increase in the magnetic field to this value leads to a decrease in the resonance amplitude and an increase in the resonance width. In the field region above B_c, the spin resonance disappears completely. Such behavior of the spin resonance is most likely due to the formation of domains with different spin polarizations in the electron system.