The solution energy of H and He in various interstitial and substitution positions in the hcp lattice of α-Ti has been calculated based on the method of electron density functional. The lowest solution energy of He corresponds to the basal octahedral position and that of H corresponds to the octahedral position (next in energy is the tetrahedral position). The calculated vibration frequencies of H in various positions are used for identification of lines in the vibration spectrum obtained by the method of neutron inelastic scattering. Taking into account these spectra, it can be concluded that hydrogen atoms occupy in the hcp lattice of Ti both the octahedral and tetrahedral positions even at 600 K. The available experimental data do not contradict the conclusion that the octahedral position is more preferable in α-Ti. The energy barriers are estimated for various diffusion paths of H and He.
The current–voltage characteristics of superconductor–insulator–semiconductor (S1–I–S2) tunnel junctions, where superconducting electrode S2 is a thin nanowire, are studied experimentally. The observed blurring of the gap singularities is interpreted as a manifestation of the order parameter quantum fluctuations. We propose a model taking into account the broadening of the density of states due to the interaction of electrons with the Mooij–Schön plasmon mode emerging in a quasi-one-dimensional superconducting channel in the regime of quantum fluctuations of the order parameter. The model gives results that are in a reasonable qualitative agreement with the experimental data.
The contribution of electron–phonon scattering to conductivity of a quantum cylinder in a lon-gitudinal magnetic field has been studied. It has been shown that the conductivity of the nanotube undergoes Aharonov–Bohm oscillations with variations in the magnetic flux through the nanotube cross section. The formulas describing the temperature dependence of the resistance of the nanostructure both in the case of an isotropic phonon spectrum and with allowance for the effects of phonon confinement have been obtained in the analytical form.
An important role of the morphology of a superconducting layer in the superconducting spin-valve effect has been established. The triplet pairing induced by the superconductor/ferromagnet proximity effect has been experimentally investigated for samples CoO x /Py1/Cu/Py2/Cu/Pb (where Py = Ni 0.81 Fe 0.19 ) with a smooth superconducting layer. The optimization of the parameters of this structure has demonstrated a complete switching between the normal and superconducting states with a change in the relative orientation of magnetizations of the ferromagnetic layers from the antiparallel to orthogonal orientation. A pure triplet contribution has been observed for the sample with a permalloy layer thickness at which the superconducting spin-valve effect vanishes. A direct comparison of the experimental data with the theoretical calculation of the temperature of the transition to the superconducting state has been performed for the first time.
Volt-ampere characteristics of narrow superconducting titanum wires have been studied experimentally. The narrowest specimens measured by means of high-resistance contacts have revealed a behavior nontrivial for superconductors: the Coulomb blockade. The Coulomb gap size correlates with the frequency of quantum phase slips. The observation confirms the identity of quantum dynamics of charge in the Josephson junctions and in the quasi-one-dimensional superconducting channels in the regime of quantum fluctuations of the order parameter.
High-quality aluminum films on GaAs substrates are studied experimentally. The critical temperature of superconductivity is found to increase markedly with decreasing the film thickness. The observed phenomenon is considered as a manifestation of the quantum confinement effect, which affects both the density of states and the electron–phonon interaction.
A numerical and analytical investigation of thermodynamic properties of a magnetized superconducting quantum cylinder has been carried out. The dependence of the difference in the magnetizations of the superconducting and normal phases on the parameters of the nanotube,temperature, and magnetic field has been analyzed. The jump in the heat capacity of the superconducting and normal states at the critical temperature has been calculated. The fluctuation contribution to the thermodynamic properties of the nanotube at a temperature abovethe transition point has been studied.
The specific features of the structure in a polycrystalline anion-deficient strontium ferrite SrFeO3 – δ have been studied at different oxygen contents by the Mössbauer spectroscopy, X-ray diffraction, and scanning electron microscopy. Three compounds with different compositions have been prepared in the dependence on the condition of heat treatment. Within each of the structures, there are several nonequivalent positions of Fe corresponding to different valence states of Fe and different local oxygen environments, the relation and the degree of distortion of which are changed in the dependence on the oxygen content. Based on the Mössbauer data, the oxygen content in each of the structures is estimated. Yet another ideal Sr16Fe16O45 composition of the SrFeO3 – δ compound is proposed for an intermediate composition in addition to those available in the literature.
We studied the structure, IR absorption spectra, the spectral characteristics of photoluminescence and morphology of cerium- and terbium-doped orthoborates of gadolinium and yttrium obtained by hydrothermal synthesis at 200°C, as well as solid solutions of orthoborates on the basis of yttrium, gadolinium, and lutetium with composition RECe0.01Tb0.1BO3 (RE = Lu0.5Gd0.39, Lu0.5Y0.39, and Y0.5Gd0.39). The X-ray diffraction spectrum of yttrium orthoborate Y1 – x – yCexTbyBO3 is described by a hexagonal lattice with space group P63/m, which, after annealing at 970°C, transforms into a monoclinic lattice with space group C2/c. High-temperature annealing of the studied orthoborates leads to a multiple, more than two orders of magnitude, increase in the luminescence intensity of Tb3+ ions when the samples are excited in the absorption band of cerium ions. This effect is the result of a significant increase in the concentration of Ce3+ ions in the orthoborates at high temperatures. It is shown that the luminescence of terbium ions is due to energy transfer from Ce3+ to Tb3+, which proceeds with high efficiency (∼85%) by the mechanism of dipole-dipole interaction between cerium and terbium.
The current–voltage characteristics of superconductor–insulator–semiconductor (S1–I–S2) tunnel junctions, where superconducting electrode S2 is a thin nanowire, are studied experimentally. The observed blurring of the gap singularities is interpreted as a manifestation of the order parameter quantum fluctuations. We propose a model taking into account the broadening of the density of states due to the interaction of electrons with the Mooij–Schön plasmon mode emerging in a quasi-one-dimensional superconducting channel in the order parameter quantum fluctuation
Structures with spiral antiferromagnets are proposed as superconducting memory elements. The first structure consists of one superconducting layer and one magnetic layer with a spiral magnetization. The latter is a Josephson junction with spiral magnet as a weak link. The schematic diagram of switching between logic states in proposed structures is described.
The thin-film structures made of LiNbO3 and obtained via laser ablation and magnetron sputtering are studied with volt-farad and volt-ampere characteristics. A potential barrier on the Si–LiNbO3 interface was found for both types of the films with the capacitance-voltage characteristics. The current-voltage characteristics showed that there are several conduction mechanisms in the structures studied. The Poole–Frenkel effect and the currents limited by a space charge mainly contribute to the electrical conductivity in the LiNbO3 film produced with the laser ablation method. The currents limited by a space charge contribute to the main mechanism in the film heterostructure obtained with the magnetron sputtering method.