JETP Letters最新文献

A nonlinear selective reflection from the boundary between a transparent dielectric and dense Rb vapor has been investigated, where the dipole broadening of the 5S_1/2–5P_3/2 working transition is significantly larger than the contribution of the Doppler width. A tunable probe laser and a pump laser with a fixed frequency have been used in the experiment. At a high intensity of pump radiation, a dip has appeared in the reflection spectrum, which splits the spectrum into two symmetric resonances. The splitting value is twice the Rabi frequency. The observation of a narrow structure corresponding to the dressed atomic states opens up additional possibilities for the study of many-particle interactions.

A series of new layered arsenides Ba(Cr_1–xCo_x)₂As₂ with x = 0, 0.2, 0.3, 0.6, 0.8, and 1.0 has been studied by ⁵⁹Co and ⁷⁵As NMR spectroscopy. The hyperfine magnetic field on the ⁷⁵As nuclei in the BaCr₂As₂ sample is absent due to the mutual compensation of hyperfine magnetic fields from neighboring magnetic Cr atoms. The mutual compensation of local magnetic fields on ⁷⁵As nuclei in compounds with x = 0.2, 0.3, and 0.6 is disturbed, and a significant broadening of the line is observed, indicating the emergence of local magnetic fields of about 0.3–0.8 T on arsenic nuclei. With an increase in the Co content to 80%, the magnetic broadening of the ⁷⁵As NMR line disappears completely, and the isotropic shift ⁷⁵K_iso increases to 0.19%. This indicates the predominance of the Knight term due to conduction electrons in the total shift. The isotropic shift ⁷⁵K_iso is maximal in the extreme BaCo₂As₂ compound, which indicates the maximum value of the density of states at the Fermi level. ⁵⁹Co NMR in Ba(Cr_0.7Co_0.3)₂As₂ in zero external magnetic field measured for the first time has demonstrated a wide distribution of the intensity of the spin echo in the frequency range of 10‒55 MHz, corresponding to a local magnetic field of several Tesla on cobalt. This field is 5–7 times lower than the characteristic local fields detected in Co-based magnets, which indicates a significant reduction of  the magnetic moment of cobalt in the Ba(Cr_0.7Co_0.3)₂As₂ compound. Starting from a cobalt content of 80%, the ⁵⁹Co NMR line is sharply narrowed, which indicates the nonmagnetic state of Co in the Ba(C-r_1‒xCo_x)₂As₂ compounds with x > 0.6.

A two-dimensional model of antiferromagnetic systems near the phase transitions of spin density waves has been considered taking into account the superconducting phase. Particular attention has been paid to the study of the influence of nonlinear effects, in particular, the interaction constant of the order parameter fluctuations, on the phase transitions arising in the system.

Resonant laser fluorescence on the Stark structure of levels of fast atoms in diagnostic beams in a nuclear fusion plasma has been theoretically studied. A nonstationary kinetic model of the population of Stark sublevels has been developed to describe resonant laser fluorescence depending on the parameters of the diagnostic beam, plasma, laser pulse, and time. The change in the fluorescence signal at the beam depending on the time and density of the plasma has been examined. The suppression of resonant laser fluorescence under both broadband and selective laser pumping of Stark sublevels with an increase in density and the tendency of nonstationary dynamic populations to statistical values, which follow from the Schrödinger theory of the Stark effect and do not depend on the density and nature of the equilibrium between the levels, has been revealed. The results are of general physical interest in the light of experimental confirmation of Schrödinger quantum theory of hydrogen-like systems, as well as in view of the relevance of the search for new possibilities for laser-beam plasma diagnostic.

The dynamics of strong plane shock waves (SW) was studied being generated in a hypersonic laser-driven shock tube (LDST) during the acceleration of thin polymer CH films by the ablation pressure of plasma produced by UV pulses of KrF laser (100 J and 100 ns). The LDST has a square cross-section of 7 × 7 mm and a length of 50 mm. At an incident radiation energy density of 70 J/cm² and intensity of 0.7 GW/cm², the SW velocity in air at atmospheric pressure of 2.6 km/s (Mach number M = 8.2) was constant while it propagated in the LDST, and it increased by an additional 30−50% when the laser plasma was confined by a transparent quartz plate. It was shown that the time of quasi-stationary propagation of the SW in the LDST is ~20 μs, being determined by the energy density of the laser pulse imparted to the plasma piston. For comparison, the SW velocity in free space quickly attenuated due to the lateral expansion of the gas, while the SW front acquired the hemispherical shape.

The energies and decay properties of the ground and lower excited levels of the ⁹C nucleus have been calculated with the no-core shell model using the cluster channel orthogonal function method we have developed. Using these data, the cross sections for the ⁸B(p, γ)⁹C radiative capture have been calculated and the astrophysical S factor has been analyzed in a wide range of collision energies. A strong dependence of the S factor at zero energy on positive parity levels in the spectrum of the ⁹C nucleus has been demonstrated.

Silica–aqueous interfaces are the foundation of electrokinetics, microfluidics, and countless physics and biophysics experiments. Yet despite their ubiquity, their molecular structure and electrostatics under flow conditions remain poorly understood. Here we use second-harmonic microscopy combined with Raman spectroscopy in glass microcapillaries, to directly track surface potential dynamics during pH cycling. Acidic and basic transitions from neutral pH conditions drive the interface along distinct kinetic pathways: forward pH jumps elicit instantaneous responses, whereas reverse relaxations are markedly slower, producing path-dependent hysteresis. Extended pH cycling experiments reveal that the silica interface can occupy multiple quasi-stable charge states with surface potential variation from –110 to –25 mV along distinct acid- and base-mediated pathways. Such history-dependent behavior has broad consequences wherever glass substrates are employed, from electrokinetic devices to single-molecule and condensed-matter studies.

We study interaction-induced backscattering mechanism for helical edge states of a two-dimensional topological insulator which is tunnel-coupled to a puddle located near the edge channel. The mechanism does not involve inelastic scattering and is due to the zero-mode fluctuations in a puddle. We discuss in detail a simple model of a puddle, which is a cavity in the bulk of the topological insulator. Such a cavity also has helical edge states with tunneling coupling to helical states encompassing the topological insulator. We analyze effect of the edge current in the puddle. Although averaged value of this current is equal to zero, its zero-mode fluctuations act, in the presence of electron–electron interaction, similar to magnetic flux thus allowing backscattering processes, which involve tunneling through the puddle. Rectification of these fluctuations leads to a finite probability of backscattering. This effect is further enhanced due to dephasing process which is also dominated by zero-mode fluctuations. Remarkably, for temperature exceeding level spacing in the puddle, the rate of backscattering does not depend on temperature in a good agreement with recent experiments.

Experiments on collisions of light nuclei at (sqrt s = 5.36) TeV have recently begun at the LHC. In this regard we make predictions for nuclear modification factor ({{R}_{{AA}}}) in 5.36 TeV C + C, O + O, and Ne + Ne collisions for scenarios with and without quark–gluon plasma formation in (pp) collisions. We find a sizeable difference in ({{R}_{{AA}}}) for these two scenarios, which grows with decreasing atomic number. This says that data on ({{R}_{{AA}}}) for light nuclei could potentially give information on the presence of jet quenching in (pp) collisions.

The topological invariant responsible for the stability of Fermi point/Fermi surface in homogeneous systems is expressed through the one particle Green’s function, which depends on momentum. It is given by an integral over the 3D hypersurface in momentum space surrounding the Fermi surface. Notion of Fermi surface may be extended to the non-homogeneous systems using Wigner–Weyl calculus. The Fermi surface becomes coordinate dependent, it may be defined as the position of the singularity in momentum space of the Wigner transformed Green’s function. Then the topological invariant responsible for the stability of this Fermi surface is given by the same expression as for the homogeneous case, in which the Green’s function is replaced by its Wigner transformation while the ordinary products are replaced by the Moyal products. We illustrate the proposed construction by the examples of the systems, in which the given topological invariant is nontrivial and may be calculated explicitly.