Possibility of local pair existence in optimally doped SmFeAsO(1-x) in pseudogap regime

We report the analysis of pseudogap Delta* derived from resistivity experiments in FeAs-based superconductor SmFeAsO(0.85), having a critical temperature T_c = 55 K. Rather specific dependence Delta*(T) with two representative temperatures followed by a minimum at about 120 K was observed. Below T_s = 147 K, corresponding to the structural transition in SmFeAsO, Delta*(T) decreases linearly down to the temperature T_AFM = 133 K. This last peculiarity can likely be attributed to the antiferromagnetic (AFM) ordering of Fe spins. It is believed that the found behavior can be explained in terms of Machida, Nokura, and Matsubara (MNM) theory developed for the AFM superconductors.Comment: 5 pages, 2 figure

Pseudogap from ARPES experiment: three gaps in cuprates and topological superconductivity

A term first coined by Mott back in 1968 a `pseudogap' is the depletion of the electronic density of states at the Fermi level, and pseudogaps have been observed in many systems. However, since the discovery of the high temperature superconductors (HTSC) in 1986, the central role attributed to the pseudogap in these systems has meant that by many researchers now associate the term pseudogap exclusively with the HTSC phenomenon. Recently, the problem has got a lot of new attention with the rediscovery of two distinct energy scales (`two-gap scenario') and charge density waves patterns in the cuprates. Despite many excellent reviews on the pseudogap phenomenon in HTSC, published from its very discovery up to now, the mechanism of the pseudogap and its relation to superconductivity are still open questions. The present review represents a contribution dealing with the pseudogap, focusing on results from angle resolved photoemission spectroscopy (ARPES) and ends up with the conclusion that the pseudogap in cuprates is a complex phenomenon which includes at least three different `intertwined' orders: spin and charge density waves and preformed pairs, which appears in different parts of the phase diagram. The density waves in cuprates are competing to superconductivity for the electronic states but, on the other hand, should drive the electronic structure to vicinity of Lifshitz transition, that could be a key similarity between the superconducting cuprates and iron based superconductors. One may also note that since the pseudogap in cuprates has multiple origins there is no need to recoin the term suggested by Mott.Comment: invited review, more info at http://www.imp.kiev.ua/~kor

Paraconductivity of K-doped SrFe2As2 superconductor

Paraconductivity of the optimally K-doped SrFe2As2 superconductor is investigated within existing fluctuation mechanisms. The in-plane excess conductivity has been measured in high quality single crystals, with a sharp superconducting transition at Tc=35.5K and a transition width less than 0.3K. The data have been also acquired in external magnetic field up to 14T. We show that the fluctuation conductivity data in zero field and for temperatures close to Tc, can be explained within a three-dimensional Lawrence-Doniach theory, with a negligible Maki-Thompson contribution. In the presence of the magnetic field, it is shown that paraconductivity obeys the three-dimensional Ullah-Dorsey scaling law, above 2T and for H||c. The estimated upper critical field and the coherence length nicely agree with the available experimental data.Comment: 12 pages, 5 figure

Subthreshold antiproton production in proton-carbon reactions

Data from KEK on subthreshold antiproton as well as on pi(+-) and K(+-) production in proton-nucleus reactions are described at projectile energies between 3.5 and 12.0 GeV. We use a model which considers a hadron-nucleus reaction as an incoherent sum over collisions of the projectile with a varying number of target nucleons. It samples complete events and allows thus for the simultaneous consideration of all particle species measured. The overall reproduction of the data is quite satisfactory. It is shown that the contributions from the interaction of the projectile with groups of several target nucleons are decisive for the description of subthreshold production. Since the collective features of subthreshold production become especially significant far below the threshold, the results are extrapolated down to COSY energies. It is concluded that an antiproton measurement at ANKE-COSY should be feasible, if the high background of other particles can be efficiently suppressed.Comment: 15 pages, 5 figures, gzipped tar file, submitted to J. Phys. G v2: Modification of text due to demands of referee

Геномные технологии в пульмонологии: роль микроРНК в развитии бронхиальной астмы и хронической обструктивной болезни легких

MicroRNAs (miRNAs) are small noncoding RNA molecules that affect gene expression and thus take part in the epigenetic regulation of almost all physiological and pathological processes. About 1,800 human miRNAs have been discovered to date; however, biological functions and protein targets for the majority remain to be unknown. Within the respiratory system, miRNAs contribute to the lung growth and lifelong maintenance of pulmonary homeostasis. Recently, the leading role of miRNAs in pathogenesis of various pulmonary diseases has been found, including asthma, chronic obstructive pulmonary disease (COPD) and lung cancer. Due to a significant progress in studying interactions between genes and their products and environmental factors, a great role of epigenetic variability, which is gene expression change not related to DNA damage, but could be inherited consistently, became apparent. There are three levels of epigenetic regulation corresponding to three main mechanisms: genomic (DNA methylation), proteomic (histone modification) and transcriptomic (regulation through RNA, primarily miRNA). Extending our knowledge on a role of miRNAs for the respiratory system could open new therapeutic targets and diagnostic markers for respiratory diseases, particularly asthma and COPD.МикроРНК – это малые некодирующие молекулы РНК, которые влияют на экспрессию генов и таким образом участвуют в эпигенетической регуляции практически всех физиологических и патологических процессов. Примерно 1 800 микроРНК человека на сегодняшний день открыты, однако биологическая функция и белки-мишени для большинства из них остаются неизвестными. В рамках дыхательной системы микроРНК необходимы для развития легких и поддержания легочного гомеостаза на протяжении всей жизни. В последние годы была открыта главнейшая роль микроРНК в патогенезе различных заболеваний, в т. ч. бронхиальной астмы (БА), хронической обструктивной болезни легких (ХОБЛ) и рака легкого. Благодаря значительному прогрессу в изучении взаимодействий между генами и их продуктами с факторами окружающей среды стала очевидной огромная роль эпигенетической изменчивости – изменений экспрессии генов, не связанных с нарушением структуры ДНК, однако способных устойчиво передаваться в ряду поколений. Существуют 3 уровня эпигенетической регуляции и соответственно – 3 ее основных механизма: геномный (метилирование ДНК), протеомный (модификация гистонов) и транскриптомный (регуляция посредством РНК, в первую очередь микроРНК). Успехи в понимании роли микроРНК в дыхательной системе помогут пролить свет на новые перспективы в поиске терапевтических мишеней и диагностических маркеров для заболеваний респираторной системы, в частности БА и ХОБЛ

Semiconductor Spintronics

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure