JETP Letters最新文献

Differential measurements of the fundamental constant (mu = {{m}_{e}}{text{/}}{{m}_{p}}) (the electron-to-proton mass ratio) for two sources near the Galactic Center—the Sgr B2(N) and B2(M) molecular clouds—suggest that (mu ) is lower in these clouds than its laboratory value. Based on observations of methanol (CH₃OH) emission lines in the 80–112 GHz range (data from the IRAM 30-m telescope), a weighted mean value (langle Delta mu {text{/}}mu rangle ) ( equiv ) (langle ({{mu }_{{{text{obs}}}}} - {{mu }_{{{text{lab}}}}}){text{/}}{{mu }_{{{text{lab}}}}}rangle = ( - 2.1 pm 0.6) times {{10}^{{ - 7}}}) ((1sigma )) was obtained for Sgr B2(N) at the sample size (n = 9). This value of (Delta mu {text{/}}mu ) has the same sign as the result of recent measurements of methanol lines in the higher frequency range of 542–543 GHz (data from the Herschel space telescope) for Sgr B2(N): (langle Delta mu {text{/}}mu rangle = ( - 4.2 pm 0.7) times {{10}^{{ - 7}}}) (sample size (n = 2)).

We present experimental study of the iron-free palladium based analogue of the 122 iron arsenide. Single crystals of BaPd₂As₂ with sharp superconducting transition were studied by two distinct techniques: local magnetization and Break–Junction. Local magnetization was used to obtain temperature dependence of the first critical field (({{H}_{{{text{c1}}}}})) from ({{T}_{{text{c}}}}) down to 10 mK. Extracted data was fitted with various models to obtain order parameter value and draw a conclusion about its potential symmetry. The ({{H}_{{{text{c1}}}}}(T)) data fitting with theoretical models suggested either a single (s)-wave gap with high anisotropy factor or two s-wave gaps. Multiple Andreev Reflections spectroscopy was used to determine the quantity of condensates and their order parameter amplitudes. The experimental results of Multiple Andreev Reflections showed the presence of two gap-like features. Studying Andreev spectra temperature evolution from 1.6 K up to ({{T}_{{text{c}}}}) we’ve extracted the gap temperature dependencies. Further fitting proved the presence of two superconducting condensates. The obtained evidence for two gap superconductivity in iron-free analogue of 122 iron arsenide family is reported for the first time. Despite the two gap superconducting state, the characteristic ratio of the large gap value is almost equal to that typical for Bardeen–Cooper–Schrieffer theory; this result shows that BaPd₂As₂ is a conventional superconductor unlike BaFe₂As₂.

Generation of photocurrent via photon drag effect enables very fast light detection with response time limited by momentum relaxation. At the same time, photon drag in bulk uniform samples is small by the virtue of small photon momentum. We show that the edge of metal gate placed above a two-dimensional electron system provides highly non-uniform electromagnetic field that enhances the drag effect. We study the drag photovoltage using an exact solution of diffraction problem for two-dimensional electron system with semi-infinite metal gate. We show that the only non-trivial dimensionless parameters governing the drag responsivity are the two-dimensional electron system conductivity scaled by the free-space impedance (eta ) and gate-two-dimensional electron system separation scaled by the incident wavelength (d{text{/}}{{lambda }_{0}}). For radiation with electric field polarized orthogonal to the gate edge, the responsivity is maximized for inductive two-dimensional conductivity with ({text{Im}}eta sim 1) and ({text{Re}}eta ll 1), and becomes very small for the capacitive two-dimensional conductivity. The electromagnetic ponderomotive force pushes the charge carriers under the gate at arbitrary two-dimensional conductivity, and the force direction is opposite to that at metal-two-dimensional system lateral contact. These patterns are explained by the dominant role of gated two-dimensional plasmons in the formation of photon drag photovoltage.

The numerical simulation of exact equations of motion (in conformal variables) for unsteady plane potential flows of an ideal fluid with a free surface over a strongly nonuniform bottom profile has revealed the nonlinear compression of a long wave packet undergoing Bragg reflection from a section with a smoothly increasing height of periodically located barriers. In this case, a short high packet of standing waves with sharp crests is formed and is then transformed into a backward wave. It is essential that the effect as a function of the frequency of the incident wave is insignificant in the middle of the barrier-induced spectral gap, but is maximal closer to its upper edge, when the forward wave penetrates deeply into the scattering region and forms, together with the appearing backward wave, a semblance of a Bragg soliton for some time interval.

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.