JETP Letters最新文献

The molecular beam epitaxy grown metamorphic heterostructures with InAs/InGaAs quantum dots emitting in the wavelength range of ( sim )1.55 μm were studied using structural and optical characterization techniques. These heterostructures contain In_xGa_{1 – x}As/GaAs(001) metamorphic buffer layers with different thickness and composition profiles. The maximum In content in the compositionally graded In_xGa_{1 – x}As layer was ({{x}_{{max }}} = 0.44) with its thickness varying in the range from 220 to 1100 nm. A correlation was established between the observed features in the photoreflectance and photoluminescence spectra and parameters of the metamorphic heterostructures. It is shown that the highest-energy S-shaped feature in the photoreflectance spectra is associated with transitions in the In_xGa_{1 – x}As inverse layer located near the structure surface. The shoulder observed in the low-temperature photoluminescence spectra on the short-wavelength side of the broad peak associated with emission from InAs/InGaAs quantum dots can be attributed to transitions from the upper part of the In_xGa_{1 – x}As metamorphic buffer layer.

Exchange scattering of electrons by neutral donor impurities in semiconductors is examined. It is shown that the difference between the cross sections for different spin configurations is significant at realistic parameter values and can play an important role in the transport properties of semiconductor heterostructures. The possibility of using the exchange scattering mechanism to orient the spins of localized electrons and nuclei under optical pumping is discussed, which is of interest for both fundamental research and the development of spintronics.

Femtosecond pulse generation modes in a Cr:forsterite laser cavity have been studied, taking into account intracavity losses caused by changes in the crystal temperature, which affect the central wavelength of the generated pulse. A numerical model has been developed taking into account the key features of Cr:forsterite lasers. Good agreement between the simulated and experimental spectra has confirmed the validity of the model. The spectral positions of the first- and second-order Kelly sidebands facilitate the accurate determination of the cavity dispersion at phase-matching points and confirm the soliton generation regime. Analysis of the gain and losses of the cavity elements has shown that the increase in the generated pulse energy with decreasing crystal temperature is caused by both an increase in the laser level lifetime and an increase in the gain cross section due to a change in the central wavelength of the generated pulse.

Superconducting spin valve heterostructures of the F1/F2/S design, consisting of superconducting (S) and ferromagnetic (F) layers, have been studied in order to detect the theoretically predicted state of solitary superconductivity. This state is characterized by the occurrence of superconductivity only at the antiparallel magnetizations of the ferromagnetic layers. In this work, owing to optimally selected design parameters of the superconducting spin valve, the state of solitary superconductivity has been experimentally realized for the first time. An anomalously large spin valve effect (Delta {{T}_{{text{c}}}} = T_{{text{c}}}^{{{text{AP}}}} - T_{{text{c}}}^{{text{P}}} > 0.2) K, which can reach a value of 1.6 K in a magnetic field of 1 kOe, has been detected in an HA/HA/Pb superconducting spin valve (where HA is a Heusler alloy Co₂Cr_{1 – x}Fe_xAl). Until now, comparable results in terms of the superconducting spin valve effect have been observed only in structures with triplet superconductivity in external magnetic fields significantly exceeding 1 kOe. The obtained results open new prospects for the development of superconducting current control devices.

The properties of plasma excitations (plasmons) in freely suspended graphene in zero magnetic field are studied for the first time using inelastic light scattering. The dependences of the plasmon energy E_PL on the electron density n and wave vector q are measured. It is shown that the dependence of the plasmon energy on the electron density is close to E_PL ~ n^1/4. The dispersion of plasma excitations in suspended graphene with a nearby gate is measured. It is found that the plasmon energy for small wave vectors depends linearly on the momentum transfer, while the dispersion for large wave vectors is described by the law E_PL ~ q^1/2. It is shown that the effective dielectric constant, which enters the dispersion relation of plasma excitations for large q, turns out to be close to 5.1 rather than unity, as might be expected for the case of freely suspended graphene. The unexpectedly large renormalization of the effective dielectric constant discovered in freely suspended graphene may probably be associated with a large interband contribution to the effective screening of Coulomb interaction.

A theory of the phonon mechanism of the anomalous Hall effect in a superconductor with p-wave electron pairing has been developed. It has been shown that the relaxation of elementary excitations of the superconductor with the emission of acoustic phonons under certain conditions imposed on the temperature and resistivity of the superconductor in the normal phase should contribute to the Hall conductivity comparable to the contribution of skew electron scattering by impurity centers.

Thermocapillary rupture of liquid films due to Marangoni convection, which is caused by thermally induced surface tension gradients along the liquid–gas interface, is examined. It is shown that the critical temperature difference at the free boundary required for rupture increases with the film thickness due to the competition between thermocapillary forces and gravity. The analysis also includes the effects of evaporation and liquid redistribution during heating. Based on our own and published data, a correlation is obtained for the first time to describe the rupture threshold in terms of the critical Marangoni number and the dimensionless film thickness. The proposed correlation allows for the prediction of film rupture conditions over a wide range of physical parameters, which is of importance for preventing critical phenomena in film cooling technologies.

The magnetization dynamics of an LC-shunted superconductor–ferromagnet–superconductor φ₀ junction is investigated in the case where the frequencies of the ferromagnetic and parallel resonances are close to each other. The calculated current–voltage characteristics and magnetization dependences of the ferromagnetic layer on the current through the junction correlate with the corresponding time dependences of the magnetization m_y(t) and voltage V(t). A unique possibility of stabilizing the magnetization precession by LC shunting in a fairly wide range of currents through the junction is demonstrated.

A microscopic method for calculating phenomenological effective polarization charges: (i) of nucleons (e_{{{text{eff}}}}^{{SM}}) and (ii) of virtual static isoscalar and isovector EL transitions (e_{{{text{is}}}}^{{SM}}) and (e_{{{text{iv}}}}^{{SM}}) obtained by fitting to the experiment in modern calculations within the many-particle shell model with a limited model space is considered. The method is based on the theory of finite Fermi systems developed by Migdal. The used approximation of separable forces has strongly simplified calculations. The ({{e}^{{SM}}}) values for ²⁰⁸Pb and ¹²⁰Sn have been calculated for the first time and compared with phenomenological values. Our results demonstrate the necessity and possibilities for further microscopic analysis of the obtained ({{e}^{{SM}}}) values in the process of generalization and development of the theory of finite Fermi systems.

The dynamics of level populations in a quantum memristor on ultracold ¹⁷¹Yb⁺ ions has been analytically considered for the case where the acting laser pulses resonant to the transitions between the levels are significantly separated in time. It has been shown that the dynamics of the level populations, as well as the control parameter of the memristor, can be calculated analytically in this case. Comparison has shown that the obtained dependences are in good agreement with the direct numerical solution of the system of equations for level population amplitudes.