Triple-gap superconductivity of MgB2 - (La,Sr)MnO3 composite. Which of the gaps is proximity induced?

Interplay of superconductivity and magnetism in a composite prepared of the ferromagnetic half-metallic La_0.67Sr_0.33MnO (LSMO) nanoparticles and the conventional s-wave superconductor MgB_2 has been studied. A few principal effects have been found in bulk samples. With an onset of the MgB_2 superconductivity, a spectacular drop of the sample resistance has been detected and superconductivity has been observed at temperature up to 20K. Point-contact (PC) spectroscopy has been used to measure directly the superconducting energy coupling. For small voltage, an excess current and doubling of the PC's normal state conductance have been found. Conductance peaks corresponding to three energy gaps are clearly observed. Two of these gaps we identified as enhanced \Delta_{\pi} and \Delta_{\sigma} gaps originating from the MgB_2; the third gap \Delta_{tr} is more than three times larger than the largest MgB_2 gap. The experimental results provide unambiguous evidences for a new type of proximity effect which follows the phase coherency scenario of proximity induced superconductivity. Specifically, at low temperature, the p-wave spin-triplet condensate with pairing energy \Delta_{tr} is essentially sustained in LSMO but is incapable to display long-range supercurrent response because of a phase-disordering state. The proximity coupling to MgB_2 restores the long-range phase coherency of the triplet superconducting state, which, in turn, enhances superconducting state of the MgB_2.Comment: 10 pages, 6 figure

Antiferromagnetic order and dielectric gap within the vortex core of antiferromagnetic superconductor

The structure of a superconducting vortex has been studied theoretically for a dirty antiferromagnetic superconductor (AFSC), modelling an AFSC as a doped semi-metal with s-wave superconducting pairing and antiferromagnetic (dielectric) interaction between electrons (holes). It is also supposed that the quasiparticles dispersion law possesses the property of nesting. The distribution of the superconducting and magnetic order parameters near the vortex core is calculated. It is shown that the antiferromagnetic order, been suppressed at large distances, is restored around the superconducting flux and the vortex core is in fact insulating and antiferromagnetic, in stark contrast to the normal metal cores of traditional superconductors. Moreover, our model calculations predict that as the temperature decreases the flux region of the superconductivity and antiferromagnetism coexistence increases.Comment: 9 pages, 3 Postscript figures,NATO Advanced Research Workshop on "Vortex dynamics in superconductors and other complex systems" Yalta, Crimea, Ukraine, 13-17 September 200

The influence of various factors on recovery process of motor control of paretic limbs muscles in patients with pyramidal syndrome

In order to study the specific features of central nervous system reaction to restoration of the cranial vault bone defects by distraction, osteosynthesis method, the electroneuromyographic examination was performed in 28 patients of 16—62 years (average age — 40,1 ± 2,6 years) with pyramidal syndrome in late recovery or residual period, of the disease (severe brain injury cerebral stroke). The main trends in electroneuromyographic indice — "cerebrospinal index" — in patients during the replacement process of post-traumatic or simulated cranial vault bone defects using transosseous distraction osteosynthesis were analyzed. The specific features of the central nervous system responses to surgical treatment, age, etiology, the brain structures initial lesion severity and disease duration were studied. As the results of the research it was established that replacement of defects of calvarium bones by transosseous distraction osteosynthesis in patients with consequences of craniocerebral trauma or stroke had. more intensive positive influence on motor zones of cerebral cortex, that shows itself in increase of effectiveness of motor control, in middle age people, at traumatic etiology of disease, at moderate pyramidal insufficiency and. at remoteness of the disease up to 1 year. Obtained data is expedient to take into account at primary selection of patients for operative treatment

BILATERAL INTERRELATIONS OF ENMGAND EEG-CHARACTERISTICS OF PYRAMID INSUFFICIENCY IN PATIENTS WITH THE CONSEQUENCES OF STROKE AND OF BRAIN INJURY

The aim. of the work was to estimate the degree of intensity of interhemispheric interaction with use of complex neurophysiological (electroneuromyography, electroencephalography) testing of 163 patients of 12—74 years in residual period, of ischemic (n = 108) and hemorrhagic (n = 22) hemispheric stroke and. severe craniocerebral injury with brain contusion (n = 33). Obtained, data testifies to the distinct negative influence of postinsult/ posttraumatic cerebral defect on functional characteristica of counter-lateral ("intact") hemisphere that is reflected in proportional changes of all the spectrum, of analyzed, neurophysiological signs. These changes affects all the tested, modules of neuromotor system, and. can be observed over a long period, after the stroke or craniocerebral injury

Layered ferromagnet-superconductor structures: the π\pi state and proximity effects

We investigate clean mutilayered structures of the SFS and SFSFS type, (where the S layer is intrinsically superconducting and the F layer is ferromagnetic) through numerical solution of the self-consistent Bogoliubov-de Gennes equations for these systems. We obtain results for the pair amplitude, the local density of states, and the local magnetic moment. We find that as a function of the thickness $d_F$ of the magnetic layers separating adjacent superconductors, the ground state energy varies periodically between two stable states. The first state is an ordinary "0-state", in which the order parameter has a phase difference of zero between consecutive S layers, and the second is a "$\pi$-state", where the sign alternates, corresponding to a phase difference of $\pi$ between adjacent S layers. This behavior can be understood from simple arguments. The density of states and the local magnetic moment reflect also this periodicity.Comment: 12 pages, 10 Figure

Inhomogeneous magnetism induced in a superconductor at superconductor-ferromagnet interface

We study a magnetic proximity effect at superconductor (S) - ferromagnet (F) interface. It is shown that due to an exchange of electrons between the F and S metals ferromagnetic correlations extend into the superconductor, being dependent on interface parameters. We show that ferromagnetic exchange field pair breaking effect leads to a formation of subgap bands in the S layer local density of states, that accommodate only one spin-polarized quasiparticles. Equilibrium magnetization leakage into the S layer as function of SF interface quality and a value of ferromagnetic interaction have also been calculated. We show that a damped-oscillatory behavior versus distance from SF interface is a distinguished feature of the exchange-induced magnetization of the S layer.Comment: 10 pages, 7 Postscript figure

Визначення вмісту антоціанів і танінів у аронії чорноплідної плодах

Introduction. Aronia melanocarpa is widely cultivated in Ukraine as a food, medicinal and ornamental plant. The quality of fresh fruit of Aronia melanocarpa was regulated by the requirements of the pharmaceutical article 42-66-87 "Fresh fruit of Aronia melanocarpa", but the article required a revision using modern approaches to the standardization of medicinal plant material.The aim of the study – determination of the content of anthocyanins and tannins in fresh and dried fruit of Aronia melanocarpa for inclusion the results of the research in the section of the monograph "Quantitative determination".Research Methods. The determination of the content of anthocyanins and tannins in fresh and dried fruit of Aronia melanocarpa was carried out by the method of absorption spectrophotometry.Results and Discussion. The content of anthocyanins in fresh fruit of Aronia melanocarpa is from (0.45±0.01) % to (0.56±0.02) % in terms of cyanidin-3-O-glucoside chloride, the content of tannins in dried fruit of Aronia melanocarpa is from (1.51±0.02) % to (2.41±0.03) % in terms of pyrogallol and dry raw materials. Therefore we proposed to enter the indicator: the content of anthocyanins – at least 0.40 % in terms of cyanidin-3-O-glucoside chloride to the national monograph "Fresh fruit of Aronia melanocarpaN", and the indicator: the content of tannins – not less than 1.5 % in terms of pyrogallol and dry raw materials to the national monograph "Dried fruit of Aronia melanocarpaN".Conclusion. By the method of absorption spectrophotometry in fresh fruit of Aronia melanocarpa the content of anthocyanins was determined, in dried fruit of Aronia melanocarpa – tannins. The results of the research were used during the development of the national monographs "Fresh fruit of Aronia melanocarpaN" and "Dried fruit of Aronia melanocarpaN".Вступление. Арония черноплодная (Aronia melanocarpa) широко культивируется в Украине как пищевое, лекарственное и декоративное растение. Качество плодов аронии черноплодной свежих регламентировалось требованиями ФС 42-66-87 “Плоды аронии черноплодной (рябины черноплодной) свежие”, однако статью необходимо было пересмотреть с использованием современных подходов к стандартизации лекарственного растительного сырья.Цель исследования – определить содержание антоцианов и танинов в плодах аронии черноплодной свежих и высушенных для включения результатов исследований в раздел монографии “Количественное определение”.Методы исследования. Содержание антоцианов и танинов в аронии черноплодной плодах свежих и высушенных определяли методом абсорбционной спектрофотометрии.Результаты и обсуждение. Содержание антоцианов в аронии черноплодной плодах свежих составляет от (0,45±0,01) до (0,56±0,02) % в пересчете на цианидин-3-O-глюкозида хлорид, содержание таниновв аронии черноплодной плодах высушенных – от (1,51±0,02) до (2,41±0,03) % в пересчете на пирогаллол и сухое сырье. Поэтому в национальную монографию “Аронии (рябины) черноплодной плоды свежиеN”предложено ввести показатель: содержание антоцианов – не менее 0,40 % в пересчете на цианидин-3-O-глюкозида хлорид, а в национальную монографию “Аронии (рябины) черноплодной плоды высушенныеN” – показатель: содержание танинов – не менее 1,5 % в пересчете на пирогаллол и сухое сырье.Вывод. Методом абсорбционной спектрофотометрии в плодах аронии черноплодной свежих определено содержание антоцианов, в плодах аронии черноплодной высушенных – танинов. Результаты исследований использовано при разработке национальных монографий “Аронии (рябины) черноплодной плоды свежиеN” и “Аронии (рябины) черноплодной плоды высушенныеN”.Вступ. Аронія чорноплідна (Aronia melanocarpa) широко культивується в Україні як харчова, лікарська і декоративна рослина. Якість аронії чорноплідної плодів свіжих регламентувалася вимогами ФС 42-66-87 “Плоди аронії чорноплідної (горобини чорноплідної) свіжі”, проте статтю треба було переглянути з використанням сучасних підходів до стандартизації лікарської рослинної сировини.Мета дослідження – визначити вміст антоціанів і танінів у аронії чорноплідної плодах свіжих та висушених для включення результатів досліджень до розділу монографії “Кількісне визначення”.Методи дослідження. Вміст антоціанів і танінів в аронії чорноплідної плодах свіжих та висушених визначали методом абсорбційної спектрофотометрії.Результати й обговорення. Вміст антоціанів у аронії чорноплідної плодах свіжих становить від (0,45±0,01) до (0,56±0,02) % у перерахунку на ціанідин-3-O-глюкозиду хлорид, вміст танінів у аронії чорноплідної плодах висушених – від (1,51±0,02) до (2,41±0,03) % у перерахунку на пірогалол і суху сировину. Тому до національної монографії “Аронії (горобини) чорноплідної плоди свіжіN” запропоновано ввести показник: вміст антоціанів – не менше 0,40 % у перерахунку на ціанідин-3-O-глюкозиду хлорид, а до національної монографії “Аронії (горобини) чорноплідної плоди висушеніN” – показник: вміст танінів – не менше 1,5 % у перерахунку на пірогалол і суху сировину.Висновок. Методом абсорбційної спектрофотометрії в аронії чорноплідної плодах свіжих визначено вміст антоціанів, у аронії чорноплідної плодах висушених – танінів. Результати досліджень використано при розробці національних монографій “Аронії (горобини) чорноплідної плоди свіжіN” й “Аронії (горобини) чорноплідної плоди висушеніN”

Theoretical study of the thermal behavior of free and alumina-supported Fe-C nanoparticles

The thermal behavior of free and alumina-supported iron-carbon nanoparticles is investigated via molecular dynamics simulations, in which the effect of the substrate is treated with a simple Morse potential fitted to ab initio data. We observe that the presence of the substrate raises the melting temperature of medium and large $Fe_{1-x}C_x$ nanoparticles ($x$ = 0-0.16, $N$ = 80-1000, non- magic numbers) by 40-60 K; it also plays an important role in defining the ground state of smaller Fe nanoparticles ($N$ = 50-80). The main focus of our study is the investigation of Fe-C phase diagrams as a function of the nanoparticle size. We find that as the cluster size decreases in the 1.1-1.6-nm-diameter range the eutectic point shifts significantly not only toward lower temperatures, as expected from the Gibbs-Thomson law, but also toward lower concentrations of C. The strong dependence of the maximum C solubility on the Fe-C cluster size may have important implications for the catalytic growth of carbon nanotubes by chemical vapor deposition.Comment: 13 pages, 11 figures, higher quality figures can be seen in article 9 at http://alpha.mems.duke.edu/wahyu

Josephson effect in double-barrier superconductor-ferromagnet junctions

We study the Josephson effect in ballistic double-barrier SIFIS planar junctions, consisting of bulk superconductors (S), a clean metallic ferromagnet (F), and insulating interfaces (I). We solve the scattering problem based on the Bogoliubov--de Gennes equations and derive a general expression for the dc Josephson current, valid for arbitrary interfacial transparency and Fermi wave vectors mismatch (FWVM). We consider the coherent regime in which quasiparticle transmission resonances contribute significantly to the Andreev process. The Josephson current is calculated for various parameters of the junction, and the influence of both interfacial transparency and FWVM is analyzed. For thin layers of strong ferromagnet and finite interfacial transparency, we find that coherent (geometrical) oscillations of the maximum Josephson current are superimposed on the oscillations related to the crossover between 0 and $\pi$ states. For the same case we find that the temperature-induced $0-\pi$ transition occurs if the junction is very close to the crossovers at zero temperature.Comment: 13 pages, 6 figure

Proximity and Josephson effects in superconductor - antiferromagnetic Nb / \gamma-Fe50Mn50 heterostructures

We study the proximity effect in superconductor (S), antiferromagnetic (AF) bilayers, and report the fabrication and measurement of the first trilayer S/AF/S Josephson junctions. The disordered f.c.c. alloy \gamma-Fe50Mn50 was used as the AF, and the S is Nb. Micron and sub-micron scale junctions were measured, and the scaling of $J_C (d_AF)$ gives a coherence length in the AF of 2.4 nm, which correlates with the coherence length due to suppression of $T_C$ in the bilayer samples. The diffusion constant for FeMn was found to be 1.7 \times 10$^{-4}$ m$^2$ s$^-1$, and the density of states at the Fermi level was also obtained. An exchange biased FeMn/Co bilayer confirms the AF nature of the FeMn in this thickness regime.Comment: 6 pages, 5 figures, accepted for Phys. Rev.