JETP Letters最新文献

Raman spectra have been measured in polycrystalline samples of La_0.5Sr_0.5FeO_3–δ and SrFeO_2.5 antiferromagnetic orthoferrites in the orthorhombic and brownmillerite phases, respectively, in the temperature range of 300–700 K. A significant decrease in the intensity of the 1300–1400 cm^–1 band when approaching the Néel temperature (T_N ~ 410 K in the substituted orthoferrite La_0.5Sr_0.5FeO_3–δ and T_N ~ 670 K in the brownmillerite SrFeO_2.5) indicates magnetic ordering in the crystals under normal conditions, and the band itself is due to two-magnon scattering, in contrast to the ~1100-cm^–1 biphonon scattering band, which retains its intensity over the entire temperature range.

The total blockade effect is an interference quantum effect reducing the two-particle correlation function of the total field, while the statistics for individual fields can be arbitrary. It has been shown that the total blockade effect can be observed in the correlated system of the polariton trimer, which is the bound state of the three polariton modes.

The modification of the bulk of synthetic optical-grade sapphire by focused (NA = 0.55) 150-fs laser pulses with a wavelength of 525 nm results in the formation of 2 × 2 × 25-µm³ regions where luminescence in the 700–850 nm band, associated with the formation of multicomponent complexes involving F₂ and ({text{F}}_{2}^{{2 + }}) vacancies and Cr³⁺ ions, is enhanced. For pulse energies of 5–22.5 nJ, the sapphire crystal lattice remains undamaged, which makes this process promising for writing three-dimensional microcodes for luminescent memory with capacities as high as 10 Gbit/cm³ suitable for error-free readout under single-photon laser excitation.

Fractional quantum Hall effect states have been studied on samples with an electron system formed by two layers of two-dimensional electrons of different densities in a wide (60 nm) GaAs quantum well. The experiment has been carried out at a temperature of 45 mK in an inclined magnetic field, where these states are more pronounced. It has been established that insignificant changes in the relation between electron densities by means of gate voltages can significantly change the picture of the observed states At various combinations of electron densities in the layers, pronounced quantized plateaus in the Hall resistance R_xy = q(h/e²) with quantum numbers q = 4/5, 3/4, 3/8, and 3/7 have been detected. Using the magnetocapacitive method, it has been established that the states with q = 4/5 and 3/4 or q = 3/8 and 3/7 arise when an incompressible state in a layer with a higher electron density exists due to a jump in the chemical potential of the layer between different spin Landau sublevels, which occurs when one or two sublevels are filled with the layer electrons, respectively. It has been established that the variation of the magnetic field makes it possible to implement two states of the fractional quantum Hall effect with q = 3/8 and 3/7 in the same incompressible state in the higher-density layer, which is broadened in the field due to the transition of electrons between layers, which occurs under the variation of the field.

The paper contains a review of a recent development in the random laser generation in spatially inhomogeneous systems. The focus is on random Raman lasers, second harmonic generation and multiphoton excited laser generation. In the paper, both the basic principles of random lasing and the most interesting practical applications are considered, especially those related to the use of random lasers as radiation sources for obtaining speckle-free high-quality images and to applications in medicine being used both in deceases diagnostics and therapy. Recent experimental results of the paper authors are also presented, in particular temporal characteristics of random Raman lasers radiation.

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.