JETP Letters最新文献

This paper presents results of experimental measurements of the spectral characteristics of stimulated Brillouin scattering (SBS) in water. It is shown that, by varying the focal waist position relative to the active medium surface, one can selectively change the frequency shift and the width of the spectral line of the SBS first Stokes component, as well as the scattering efficiency. This effect opens a possibility of fine-tuning the spectral characteristics of scattering by varying the excitation geometry of the active medium.

The Frobenius covariant is used to construct a projection operator onto the spin-S eigenspaces associated with the squares of the total and orbital angular momenta. The covariant admits two equivalent representations: as a polynomial in powers of the scalar product of the spin and orbital angular momentum operators, and as a finite expansion in terms of their respective polarization operators. A correspondence is established with Villars’ angular momentum projection, used in nuclear structure studies.

Layered (Li, Fe)OHFeSe compounds are attractive due to their high-temperature superconductivity. In this work, (Li, Fe)OHFeSe samples were doped via a solvothermal method using a saturated solution of calcium glyceroxides in glycerol. Dynamic magnetic susceptibility measurements revealed that the doped samples exhibit superconductivity at a temperature of ({{T}_{c}} = 46{kern 1pt} ) K, which significantly exceeds the ({{T}_{c}} = 37{kern 1pt} ) K of the pristine samples. Based on X-ray diffraction data, it is suggested that the doping is due to the incorporation of calcium ions into the (Li, Fe)OH layers, whereas the structure of the FeSe layers in the doped (Li, Fe)OHFeSe compound remains unchanged.

The linewidth of plasma resonance in a two-dimensional electron system based on an AlGaAs/GaAs heterostructure in a magnetic field has been studied experimentally and theoretically. It has been shown that the linewidth of the bulk magnetoplasma mode increases with the magnetic field from 1/τ (where (tau ) is the electron relaxation time) in zero magnetic field up to 2/τ, which is consistent with the transition from plasma to cyclotron resonance. An analytical theoretical model has been developed to explain the observed increase in the plasma resonance linewidth in the magnetic field. The obtained results reveal the complex relaxation dynamics of plasma excitations in the presence of the magnetic field.

Cross sections for the fission of ²³⁹Pu and ²⁴⁰Pu by 0.3–500-MeV neutrons have been measured on the time-of-flight spectrometer of the GNEIS neutron complex at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute. Fission fragments have been detected using low-pressure position-sensitive multiwire proportional counters. The ²³⁹Pu(n, f) and ²⁴⁰Pu(n, f) fission cross sections have been measured relative to the ²³⁵U(n, f) fission cross section. The obtained data are compared with the results of previous experimental works, as well as with cross sections from various libraries of evaluated data.

A compact laser cooling system for transportable optical lattice clocks based on cold ¹⁷¹Yb atoms has been presented. The system size has been reduced by eliminating the first cooling stage and using compact configurations for the main subsystems of the laser cooling system. A Zeeman slower has been modeled and developed, reducing the velocity of atoms from a thermal source to a level sufficient for their direct capture in a second-stage magneto-optical trap, avoiding the first cooling stage. A method for estimating the number of atoms and their temperature in the magneto-optical trap is presented. The performance of the compact laser cooling system with the developed Zeeman slower has been experimentally confirmed: ~10^{6 171}Yb atoms with a temperature of ~35 μK have been collected in ~1 s. The achieved parameters allow for loading of ~4000 atoms into the optical lattice.

The efficient capture of thulium atoms from an atomic beam into a magneto-optical trap at the spectrally narrow 530-nm transition with a natural linewidth of 350 kHz, avoiding the primary cooling stage that is standard in many experiments, has been demonstrated. To optimize the capture parameters, a machine learning method with automated control of the experimental setup and feedback has been used, which has made it possible to achieve more than 75% capture efficiency compared to the previously used configuration. In addition, the number of atoms has been measured using 530-nm probe radiation with the ability to achieve signal-to-noise levels comparable to those obtained with fluorescence detection on the strong 410-nm transition. This significantly reduces the requirements for the 410-nm laser system, which was previously used for primary cooling and detection of atoms, simplifying the experimental setup and paving the way toward transportable thulium optical clocks.

Data on the single-spin asymmetry of inclusive charged pion production in the fragmentation region of a 26.3 GeV/c pion beam have been obtained using the results of measurements performed on a polarized target at the SPASCHARM facility at the U-70 accelerator complex (Protvino) in 2018. The average asymmetry values for π^– and π⁺ mesons have the same sign and a magnitude of 20%. This is the first measurement of the single-spin asymmetry of π⁺ mesons in the π^–p^↑ → π⁺X reaction.

Magnetoplasmons in a two-dimensional electron Fermi liquid in samples with a negligible defect density have been studied. A phenomenological generalization of the Landau Fermi liquid theory has been proposed including memory effects in electron–electron interactions in the presence of an external magnetic field. It has been shown that memory effects lead to a dissipationless contribution to the complex dispersion of magnetoplasmons, additive with the dissipative contribution due to interparticle collisions. The calculated imaginary part of the dispersion, depending on the frequency and magnetic field, can be either positive or negative. Thus, instability of magnetoplasmons due to memory effects has been predicted. It has been discussed that this instability may be a key process in the formation of both the ground state of two-dimensional electrons in a density-wave magnetic field and zero-resistance states in a radio-frequency electric field.

The article tackles the passage (channeling) of an accelerated beam of neutral Na atoms with energies of 25‒100 keV and transverse energies of 0.5–2 eV in wide cylindrical and flat aluminum channels with a smooth amorphous wall surface. It has been shown that at the channel length-to-width (radius) ratio of the order of 100, the proportion of stopping losses of atoms due to the dissipative van der Waals force can be more than 50% with a total relative energy loss (in cylindrical channels) at a level of 0.1–2%.