Microwave Response of V3Si Single Crystals: Evidence for Two-Gap Superconductivity

The investigation of the temperature dependences of microwave surface impedance and complex conductivity of V3Si single crystals with different stoichiometry allowed to observe a number of peculiarities which are in remarkable contradiction with single-gap Bardeen-Cooper-Schrieffer theory. At the same time, they can be well described by two-band model of superconductivity, thus strongly evidencing the existence of two distinct energy gaps with zero-temperature values Delta1~1.8Tc and Delta2~0.95Tc in V3Si.Comment: Submitted to Europhysics Letter

Excitonic BCS-BEC crossover at finite temperature: Effects of repulsion and electron-hole mass difference

The BCS to Bose-Einstein condensation (BEC) crossover of electron-hole (e-h) pairs in optically excited semiconductors is studied using the two-band Hubbard model with both repulsive and attractive interactions. Applying the self-consistent t-matrix approximation combined with a local approximation, we examine the properties of a normal phase and an excitonic instability. The transition temperature from the normal phase to an e-h pair condensed one is studied to clarify the crossover from an e-h BCS-like state to an excitonic Bose-Einstein condensation, which takes place on increasing the e-h attraction strength. To investigate effects of the repulsive interaction and the e-h mass difference, we calculate the transition temperature for various parameters of the interaction strengths, the e-h particle density, and the mass difference. While the transition temperature in the e-h BCS regime is sufficiently suppressed by the repulsive interaction, that of the excitonic BEC is largely insensitive to it. We also show quantitatively that in the whole regime the mass difference leads to large suppression of the transition temperature.Comment: 8 pages, 7 figures, to be published in Phys. Rev.

Strong interaction of correlated electrons with phonons: Exchange of phonon clouds by polarons

We investigate the interaction of strongly correlated electrons with phonons in the frame of the Hubbard-Holstein model. The electron-phonon interaction is considered to be strong and is an important parameter of the model besides the Coulomb repulsion of electrons and band filling. This interaction with the nondispersive optical phonons has been transformed to the problem of mobile polarons by using the canonical transformation of Lang and Firsov. We discuss in particular the case for which the on-site Coulomb repulsion is exactly cancelled by the phonon-mediated attractive interaction and suggest that polarons exchanging phonon clouds can lead to polaron pairing and superconductivity. It is then the frequency of the collective mode of phonon clouds being larger than the bare frequency, which determines the superconducting transition temperature.Comment: 23 pages, Submitted to Phys. Rev.

Concept of the right to a decent human existence as a basis for self-realization russian young people and its social and legal guarantees

В работе рассматривается философско-правовое и социально-экономическое обоснование концепции права на достойное человеческое существование, изучается ее практическая реализация в современной Российской Федерации.This paper considers the philosophical and legal and socio-economic justification of the concept of the right to a decent human existence. Study its practical implementation in the modern Russian Federation

Effect of disorder on the NMR relaxation rate in two-band superconductors

We calculate the effect of nonmagnetic impurity scattering on the spin-lattice relaxation rate in two-band superconductors with the s-wave pairing symmetry. It is found that for the interaction parameters appropriate for MgB2 the Hebel-Slichter peak is suppressed by disorder in the limit of small interband impurity scattering rate. In the limit of strong impurity scattering, when the gap functions in the two bands become nearly equal, the single-band behavior is recovered with a well-defined coherence peak just below the transition temperature.Comment: 6 pages, 4 figure

Personalized patterns of teachers training in document science course subjects in a vocational pedagogical university

The article is focused on the study of challenging issues which occur when updating methodological-pedagogical support and applying personalized educational paths in the training of future teachers of document science course subjects for intermediate vocational education institutions, as well as according to various other programmes of students training as part of the "Vocational training (by branches)" course. The key method of the given problem research is meant to be analysis and experience summarization of vocational-oriented, academic, teaching and guiding and scientific work with the students of Russian State Vocational Pedagogical University, being taught according to principal educational programme "Document management in an organization" as part of "Vocational training (by branches)" preparation as well as learning methodological approaches for creating personalized educational paths for them. Research results: developed approaches to applying personalized educational paths in the training of students in a vocational pedagogical university; drawn-up recommendations on updating methodological-pedagogical support in the training of future teachers of document science course subjects for intermediate vocational education institutions, undertaken analysis of the possible ways of improving their training. The content of the article may prove helpful for: university faculty and universities chief executives for the improvement of the training quality of future professionals, for more effective educational process organization, for forming personalized educational paths in the training of students; for chief executives of intermediate vocational education institutions where the specialized training "Document support of management and archive science" is provided; for students being trained as part of "Vocational training (by branches)" course. © Authors

The educational standards of the third generation and teaching educational discipline "Concepts of modern natural science"

В данной работе рассматриваются место и роль вспомогательных учебных дисциплин в современной концепции образования. Рассказывается об особенностях преподавания учебной дисциплины «Концепции современного естествознания».This paper discusses the place and role of auxiliary educational disciplines in modern concepts of education. Talks about the teaching of the discipline "Concepts of modern natural science"