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Superconductors
Kinds of Superconductors Selected AbstractsHybrid Organic/Inorganic Supramolecular Conductors D2[Au(CN)4] [D = Diiodo(ethylenedichalcogeno)tetrachalcogenofulvalene], Including a New Ambient Pressure SuperconductorEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2007Tatsuro Imakubo Abstract Five diiodo(ethylenedichalcogeno)tetrachalcogenofulvalenes, DIEDSS {2-(5,6-dihydro[1,3]diselenolo[4,5- b][1,4]diselenin-2-ylidene)-4,5-diiodo-1,3-dithiole}, DIET-STF {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,3]dithiolo[4,5- b][1,4]dithiine}, DIEDS-STF {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,4]diselenino[2,3- d][1,3]dithiole}, DIETSe {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,3]diselenolo[4,5- b][1,4]dithiine}, and DIEDSSe {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,3]diselenolo[4,5- b][1,4]diselenine},have been synthesized without the use of the highly toxic reagent CSe2, and their Au(CN)4 salts have been prepared by electrochemical oxidation. Characteristic I···N iodine bonds are constructed in all crystals, and their packing motifs are classified into two groups by the difference in the space group symmetry. The salt of DIEDSS crystallizes in the monoclinic C2/c space group and a novel helical supramolecular architecture is constructed by the strong and directional I···N iodine bond. On the other hand, the rest of the four salts crystallize in the triclinic P space group and their donor packing motifs belong to the so-called ,-type. Conducting properties of the ,-type salts strongly depend on the number and positions of the selenium atoms on the donor molecule. The salts based on the diselenadithiafulvalene (DSDTF) derivatives, DIET-STF and DIEDS-STF, show metal,semiconductor transition and the salt of fully selenated ,-donor DIEDSSe shows stable metallic behavior down to 1.6 K. On the other hand, (DIETSe)2[Au(CN)4] is semimetallic down to low temperature and the superconducting transition occurs at around 2 K (onset).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Design and Nanofabrication of Superconductor Ceramic Strands and Customized LeadsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2004Anatoly E. Rokhvarger We made possible an engineering application of the 18-year-old Nobel Prize-winning discovery of High Temperature Superconductor (HTS) ceramic particles. Guided by certain theories of physics and nano-science, we created the ceramic-silicone nanofabrication method where a silicone additive controls both the nanostructural evolution of the magnetically oriented HTS ceramic nano-grains by a 3D polymeric matrix scaffold and thermally induced nano-phase transformation. These result in the sintered granular superconductor ceramic composite material with the desirable superconducting nano-phase composition and 3D nanostructure including vortex-pinning network. The prototype HTS samples were nanofabricated in the form of adhesion substrate coated strands or surfaces or variously shaped bulk leads. [source] ChemInform Abstract: A New Triclinic Modification of the Pyrochlore-Type KOs2O6 Superconductor.CHEMINFORM, Issue 24 2009S. Katrych Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Synthesis of a New Member in Iron-Based Layered Superconductor: Nd0.8Th0.2OFeAs with Tc = 38 K.CHEMINFORM, Issue 9 2009Min Xu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Iron-Based Layered Superconductor: LaOFeP.CHEMINFORM, Issue 45 2006Yoichi Kamihara Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis and Characterization of La Doped MgB2 Superconductor.CHEMINFORM, Issue 39 2004C. Shekhar Abstract For Abstract see ChemInform Abstract in Full Text. [source] Microstructural, thermal, and electrical properties of Bi1.7V0.3Sr2Ca2Cu3Ox glass-ceramic superconductorCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2004T. S. Kayed Abstract A glass-ceramic Bi1.7V0.3Sr2Ca2Cu3Ox superconductor was prepared by the melt-quenching method. The compound was characterized by scanning electron microscopy, x-ray diffraction, differential thermal analysis, current-voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x-ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 °C while the activation energy for crystallization of glass has been found to be Ea = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset Tc of 80 K was measured and the onset Tc was 100 K. The Hall resistivity ,H was found to be almost field-independent at the normal state. A negative Hall coefficient was observed and no sign reversal of ,H or RH could be noticed. The mobility and carrier density at different temperatures in the range 140-300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Yttrium ,-Diketonate Glyme MOCVD Precursors: Effects of the Polyether Length on Stabilities, Mass Transport Properties and Coordination SpheresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2004Graziella Malandrino Abstract The glyme adducts of trishexafluoroacetylacetonato yttrium, [Y(hfa)3·monoglyme], [Y(hfa)3·diglyme], [Y(hfa)3·(H2O)2·triglyme] and [Y(hfa)2·tetraglyme]+[Y(hfa)4], {CH3(OCH2CH2)nOCH3, n = 1 monoglyme, 2 diglyme, 3 triglyme and 4 tetraglyme}, were synthesized and characterized by elemental analysis, mass spectrometry, and IR, 1H and 13C NMR spectroscopy. Additionally, [Y(hfa)3·monoglyme] and [Y(hfa)3·diglyme] were characterized by single-crystal X-ray diffraction studies. The mass-transport properties of these adducts were investigated by thermogravimetric analysis, differential scanning calorimetry, evaporation-rate measurements and chemical vapour-deposition experiments. There is evidence of high volatility and very good thermal stabilities with a residue lower than 2,4 %. Vaporization-rate experiments proved that all adducts are well-suited for metal-organic chemical vapour-deposition experiments. The [Y(hfa)3·monoglyme] complex was successfully applied in the low-pressure MOCVD process of YBaCuO HTc superconductor using a multimetal molten single source. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Research and Prospects of Iron-Based SuperconductorsADVANCED MATERIALS, Issue 45 2009Zhi-An Ren Abstract The discovery of a new superconductor, LaFeAsO1,xFx with a superconducting critical temperatureT,c, of 26,K in 2008, has quickly renewed interest in the exploration of iron-based superconductors. More than 70 new superconductors have been discovered within several months, with the highest Tc of up to 55,K being observed in the SmFeAsO1,x compound. High Tcs have previously only been observed in cuprates; these new iron-based superconductors have been added as second members of the high- Tc family. The crystal structure of these compounds contains an almost 2D Fe,As layer formed by FeAs4 tetrahedrons, which can be separated by an oxide or metal layer that provides extra electrons to the Fe,As layer, and the itinerant iron 3d electrons form an antiferromagnetic (AFM) order state in the undoped parent compounds at around 100,200,K. Superconductivity can be induced by carrier doping, which destroys the AFM ground state. In this Review, the most recent findings on and basic experimental facts about this class of high- Tc materials will be presented, including the various superconducting structures, the synthesis methods, the physical properties of the parent compounds, the doping methods that could produce superconductivity, pressure effects, and the prospects for this new iron-based high- Tc family. [source] Very High Critical Field and Superior Jc -Field Performance in NdFeAsO0.82F0.18 with Tc of 51 K,ADVANCED MATERIALS, Issue 2 2009Xiaolin Wang A new family of oxypnictide superconductors, LaFeAsO0.89F0.11, brings new impetus to the field of high-temperature superconductivity. In this work, we show that the upper critical field values Hc2 (48 K) = 13 T and Hc2(0) can exceed 80,230 T in a high-pressure-fabricated NdO0.82F0.18FeAs bulk sample with Tc of 51 K. We also demonstrate the superior performance of supercurrent density in fields for this new superconductor. [source] Progress in Nanoengineered Microstructures for Tunable High-Current, High-Temperature Superconducting Wires,ADVANCED MATERIALS, Issue 3 2008G. Holesinger Abstract High critical current densities (Jc) in thick films of the Y1Ba2Cu3O7,, (YBCO, Tc , 92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application-dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect-free conductor in which the grain-to-grain connectivity maintains levels of inter-grain Jc that are comparable to the intra-grain Jc. That is, high critical current (Ic) YBCO coated conductors must contain engineered inhomogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high-performance YBCO coated-conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano-engineer the microstructure for tuneable superconducting wires. Multi-scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher Ic wires for large-scale, commercial application are discussed within the context of these recent advances. [source] A New Superconducting Phase of Sodium Cobalt Oxide,ADVANCED MATERIALS, Issue 21 2004K. Takada A new superconducting sodium cobalt oxide (see Figure, left) has been synthesized through soft-chemical modification using ,-NaCoO2 as a parent compound, in place of the ,-Na0.7CoO2 used to make the first cobalt oxide superconductor (see Figure, right). A three-layer periodicity of the CoO2 stacking sequence exists in the present material, in contrast to a two-layer one in the previous. The new oxide has a superconducting transition at 4.6,K. [source] HTSC cuprate phase diagram using a modified Boson,Fermion,Gossamer model describing competing orders, a quantum critical point and possible resonance complexINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009Richard H. Squire Abstract There has been considerable effort expended toward understanding high temperature superconductors (HTSC), and more specifically the cuprate phase diagram as a function of doping level. Yet, the only agreement seems to be that HTSC is an example of a strongly correlated material where Coulomb repulsion plays a major role. This manuscript proposes a model based on a Feshbach resonance pairing mechanism and competing orders. An initial BCS-type superconductivity at high doping is suppressed in the two particle channel by a localized preformed pair (PP) (Nozieres and Schmitt-Rink, J Low Temp Phys, 1985, 59, 980) (circular density wave) creating a quantum critical point. As doping continues to diminish, the PP then participates in a Feshbach resonance complex that creates a new electron (hole) pair that delocalizes and constitutes HTSC and the characteristic dome (Squire and March, Int J Quantum Chem, 2007, 107, 3013; 2008, 108, 2819). The resonant nature of the new pair contributes to its short coherence length. The model we propose also suggests an explanation (and necessity) for an experimentally observed correlated lattice that could restrict energy dissipation to enable the resonant Cooper pair to move over several correlation lengths, or essentially free. The PP density wave is responsible for the pseudogap as it appears as a "localized superconductor" since its density of states and quasiparticle spectrum are similar to those of a superconductor (Peierls,Fröhlich theory), but with no phase coherence between the PP. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] XAFS study on a pressure-induced superconductor Cs3C60 under high pressureJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Satoshi Fujiki Cs K-edge XAFS of Cs3C60 which is a pressure-induced superconductor were measured at 21 and 34 kbar by using a diamond anvil cell (DAC) in order to obtain the structural information under high pressure, and to clarify the origin of the pressure-induced superconductivity. The distances and the mean square displacements between the Cs and C atoms are consistent with those determined by X-ray powder diffraction. Consequently, the high-pressure XAFS can give the reliable structural-information on a fullerene superconductor under high pressure. We also show the procedure of the analysis of high-pressure XAFS with DAC in detail. [source] Superfluid signatures in magnetar seismologyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009N. Andersson ABSTRACT We investigate the role of neutron star superfluidity for magnetar oscillations. Using a plane-wave analysis, we estimate the effects of a neutron superfluid in the elastic crust region. We demonstrate that the superfluid imprint is likely to be more significant than the effects of the crustal magnetic field. We also consider the region immediately beneath the crust, where superfluid neutrons are thought to coexist with a type II proton superconductor. Since the magnetic field in the latter is carried by an array of fluxtubes, the dynamics of this region differ from standard magnetohydrodynamics. We show that the presence of the neutron superfluid (again) leaves a clear imprint on the oscillations of the system. Taken together, our estimates show that the superfluid components cannot be ignored in efforts to carry out ,magnetar seismology'. This increases the level of complexity of the modelling problem, but also points to the possibility of using observations to probe the superfluid nature of supranuclear matter. [source] Phase diagram of the NdFe1,xRhx AsO superconductorPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 3-4 2010H. Y. Shi Abstract Polycrystalline samples with a nominal composition of NdFe1,xRhx AsO (0 , x , 0.25) were synthesized using a solid state reaction method. Bulk superconductivity with a maximum TC = 13 K is observed in the x = 0.1 sample. A temperature,composition phase diagram is established for the NdFe1,xRhx AsO system based on the electrical resistivity and magnetization measurements. A first-order-like transition from an antiferromagnetic state to the superconducting state at a critical Rh-doping point xC , 0.045 is observed in the present phase diagram. The value for the upper critical field ,0Hc2(0) is estimated to be about 26 T for the x = 0.10 sample by using the Werthamer,Helfand,Hohenberg theory. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Textured growth and microstructure of pulsed laser deposited Nb/Cr/SmCo5 hybrid structuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2010R. Schaarschuch Abstract Hybrid structures based on superconducting Nb and highly coercive ferromagnetic SmCo5 films grown on MgO(100) substrates were fabricated by pulsed laser deposition under UHV conditions. Thin film architectures of SmCo5 on Nb and the reversed system both with and without Cr spacer layer between superconductor and ferromagnet were examined by transmission electron microscopy and X-ray diffraction concerning their microstructure and epitaxial relationship, respectively. For SmCo5 on Nb with thick intermediate Cr spacer the epitaxial relationship MgO(001)[100]//Cr(001)[110]//Nb(001)[110]//Cr(001)[110]//SmCo5(11,,,20)[0001]//Cr(001)[110] was found. With decreasing thickness of the Cr spacer layer the strength of the texture decreases and finally crystallinity of SmCo5 is lost. In the reversed layer system, Nb on Cr on SmCo5, with decreasing thickness of the Cr spacer layer the epitaxial relationships change from SmCo5(11,,,20)[0001]//Nb(001)[110] to local SmCo5(11,,,20) [0001]//Nb(110)[1,,,11] and the Nb texture changes from the (001)[110] component to a ,110, fibre. The orientation relationships observed are discussed with regard to elastic strain energy minimization. [source] Magnetic pinning-effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 bilayerPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Daniel Hsu Abstract The vortex lines of superconductor can be driven by electrical currents, which are often coupled with a reliable control of flux quanta movement by defects or magnetic domains. In this work, the magnetic pinning-effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers is investigated. It is found that by increasing the field from 0 to 5 Tesla, the critical current Ic of pure YBCO film at 50 K is suppressed by three orders of magnitude. However, in the NCMO/YBCO bilayer Ic is less sensitive to the field and maintains at the level of 100 mA at high field. This result indicates that the magnetic pining effect of NCMO is much more efficient than the conventional routes, which maybe related to the fine domain structure of NCMO film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetoresistance, transport noise and granular structure in polycrystalline superconductorsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2007I. García-Fornaris Abstract In this work we present a theoretical study on the magnetic field dependence of the electrical resistance R (Ba) and the transport noise (TN) in a high- Tc polycrystalline superconductors. In the model, we have considered the ceramic superconductor as a series-parallel array of Josephson devices and the intergranular magnetic field is described within the framework of the intragranular flux-trapping model. The obtained results qualitatively reproduce the hysteretic behavior of the R (Ba) dependence in increasing and decreasing applied magnetic fields. We have found that the hysteretic behavior in the R (Ba) dependence changes appreciably if different statistical distributions of the geometric factors of grains are used. In addition, such changes are also reflected in the TN, which is produced by the electric current rearrangement in the array with increasing applied magnetic fields. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Feshbach shape resonance for high Tc superconductivity in superlattices of nanotubesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006Antonio Bianconi Abstract The case of a Feshbach shape resonance in the pairing mechanism for high Tc superconductivity in a crystalline lattice of doped metallic nanotubes is described. The superlattice of doped metallic nanotubes provides a superconductor with a strongly asymmetric gap. The disparity and different spatial locations of the wave functions of electrons in different subbands at the Fermi level should suppress the single electron impurity interband scattering giving multiband superconductivity in the clean limit. The Feshbach resonances will arise from the component single-particle wave functions out of which the electron pair wave function is constructed: pairs of wave functions which are time inverse of each other. The Feshbach shape resonance increases the critical temperature by tuning the chemical potential at the Lifshitz electronic topological transition (ETT) where the Fermi surface of one of the bands changes from the one dimensional (1D) to the two dimensional (2D) topology (1D/2D ETT). (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic impurity transition in a (d,+,s)-wave superconductorPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010L. S. BorkowskiArticle first published online: 8 FEB 2010 Abstract We consider the superconducting state of symmetry with finite concentration of Anderson impurities in the limit . The model consists of a BCS-like term in the Hamiltonian and the Anderson impurity treated in the self-consistent large- N mean field approximation. Increasing impurity concentration or lowering the ratio drives the system through a transition from a state with two sharp peaks at low energies and exponentially small density of states at the Fermi level to one with . This transition is discontinuous if the energy of the impurity resonance is the smallest energy scale in the problem. [source] Particle,hole asymmetry in the scanning tunneling spectroscopy of the high temperature superconductorsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2007Anna Gorczyca Abstract There is still no consensus on the mechanism that is responsible for a particle,hole asymmetry observed in scanning tunneling spectroscopy of high-temperature superconductors. According to the most popular hypothesis this asymmetry results from strong Coulomb correlations in a nearly half-filled band. In the present paper we propose another mechanism that leads to such asymmetry. It originates from the coupling between the superconductor and the substrate that the system is deposed on. We show that this coupling gives rise to the particle,hole asymmetry only in the case of an anisotropic superconductivity. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin triplet superconductivity in Sr2RuO4PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Karol I. Wysoki Abstract Sr2RuO4 is at present the best candidate for being a superconducting analogue of the triplet superfluidity in 3He. This material is a good (albeit correlated) Fermi liquid in the normal state and an exotic superconductor below Tc. The mechanism of superconductivity and symmetry of the order parameter are the main puzzling issues of on-going research. Here we present the results of our search for a viable description of the superconducting state realised in this material. Our calculations are based on a three-dimensional effective three-band model with a realistic band structure. We have found a state with non-zero order parameter on each of the three sheets of the Fermi surface. The corresponding gap in the quasi-particle spectrum has line or point nodes on the , and , sheets and is complex with no nodes on the , sheet. This state describes remarkably well a number of existing experiments including power low temperature dependence of the specific heat, penetration depth, thermal conductivity etc. The stability of the state with respect to disorder and different interaction parameters are also analyzed briefly. [source] Effects of Zn doping on YBaCuO superconductorPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006M. Mahtali Abstract In this work we present a study of Zn impurity effects on the YBa2Cu3O7,, high Tc superconducting ceramics prepared by the solid state reaction method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA) techniques, and resistivity measurements are used to characterize the YBa(Cu1,xZnx)3O7,, samples. The obtained results show that, for example, the value of the transition critical temperature is decreasing up to 80 K caused by the substitution of Zn for Cu in the interval 0 , x , 0.01. Also, the peritectic transformation of superconducting phase undergoes a displacement to lower temperatures compared with pure YBaCuO. On the basis of the obtained results, the effects of Zn doping on the structural and electronic properties are explained. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Purely electronic transport and localization in the Bose glassANNALEN DER PHYSIK, Issue 12 2009M. Müller Abstract We discuss transport and localization properties on the insulating side of the disorder dominated superconductor-insulator transition, described in terms of the dirty boson model. Analyzing the spectral properties of the interacting bosons in the absence of phonons, we argue that the Bose glass phase admits three distinct regimes. For strongest disorder the boson system is a fully localized, perfect insulator at any temperature. At smaller disorder, only the low temperature phase exhibits perfect insulation while delocalization takes place above a finite temperature. We argue that a third phase must intervene between these perfect insulators and the superconductor. This conducting Bose glass phase is characterized by a mobility edge in the many body spectrum, located at finite energy above the ground state. In this insulating regime purely electronically activated transport occurs, with a conductivity following an Arrhenius law at asymptotically low temperatures, while a tendency to superactivation is predicted at higher T. These predictions are in good agreement with recent transport experiments in highly disordered films of superconducting materials. [source] Electronic structure calculations for inhomogeneous systems: Interfaces, surfaces, and nanocontactsANNALEN DER PHYSIK, Issue 8 2008U. Schwingenschlögl Abstract The article gives an introduction into the application of density functional theory (DFT) to inhomogeneous systems. To begin with, we describe the interplay of specific materials at interfaces, resulting in structure relaxation and modifications of the chemical bonding. We address interfaces between YBa2Cu3O7 and a normal metal, in order to quantify the intrinsic interface charge transfer into the superconductor. Moreover, we study the internal interfaces in a V6O13 battery cathode and the effects of ion incorporation during the charging and discharging process. The second part of the article deals with the influence of surfaces on the nearby electronic states. Here, we investigate a LaAlO3/SrTiO3 heterostructure in a thin film geometry. We particularly explain the experimental dependence of the electronic states at the heterointerface on the surface layer thickness. Afterwards, surface relaxations are studied for both the clean Ge(001) surface and for self-assembled Pt nanowires on Ge(001). In the third part, we turn to atomic and molecular contacts. We compare the properties of prototypical Al nanocontact geometries, aiming at insight into the chemical bonding and the occupation of the atomic orbitals. Finally, the local electronic structure of a benzene-1,4-dithiol molecule between two Au electrodes is discussed as an example for a molecular bridge. [source] Current density mapping approach for design of clinical magnetic resonance imaging magnetsCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2002Stuart Crozier Abstract Novel current density mapping (CDM) schemes are developed for the design of new actively shielded, clinical magnetic resonance imaging (MRI) magnets. This is an extended inverse method in which the entire potential solution space for the superconductors has been considered, rather than single current density layers. The solution provides an insight into the required superconducting coil pattern for a desired magnet configuration. This information is then used as an initial set of parameters for the magnet structure, and a previously developed hybrid numerical optimization technique is used to obtain the final geometry of the magnet. The CDM scheme is applied to the design of compact symmetric, asymmetric, and open architecture 1.0,1.5 T MRI magnet systems of novel geometry and utility. A new symmetric 1.0-T system that is just 1 m in length with a full 50-cm diameter of the active, or sensitive, volume (DSV) is detailed, as well as an asymmetric system in which a 50-cm DSV begins just 14 cm from the end of the coil structure. Finally a 1.0-T open magnet system with a full 50-cm DSV is presented. These new designs provide clinically useful homogeneous regions and have appropriately restricted stray fields but, in some of the designs, the DSV is much closer to the end of the magnet system than in conventional designs. These new designs have the potential to reduce patient claustrophobia and improve physician access to patients undergoing scans. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 208,215, 2002 [source] Growth of single-grain GdBa2Cu3O7-x superconductors by top seeded infiltration and growth techniqueCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2010Guo-Zheng Li Abstract The top seeded infiltration and growth technique (TSIG) is an effective way for the preparation of bulk REBa2Cu3O7-x (RE-123, where RE denotes rare earth) with finely dispersed RE2BaCuO5 (RE-211) particles compared to the conventional melt growth (MG) method. The nucleation temperature and the ending growth temperature are the most important parameters need to be optimized during the preparation of RE-123 bulks by the TSIG process. In this paper, the effects of these parameters on the growth of single-grain GdBa2Cu3O7-x (GdBCO) superconductors have been investigated experimentally. It is found that the temperature for the growth of single-grain GdBCO is in the region between 1040 °C and 1015 °C. In addition, the relation between growth rate and supercooling has been investigated in detail. The combined techniques of SEM and EDS were used to study the microstructure of the samples grown at different temperatures. Based on this, a two-step slow cooling method during the crystallization process is proposed for the fabrication of RE-123 bulks. Finally, the single-grain GdBCO samples of the diameters 20 mm and 30 mm were fabricated successfully by the TSIG technique, with the slow-cooling process in the temperature window 1030 °C,1020 °C for 60 h and 100 h respectively. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fundamental characteristics and 3D electromagnetic analysis for magnetic levitation transporter using YBCO superconductorsELECTRICAL ENGINEERING IN JAPAN, Issue 2 2007Hiroshi Ueda Abstract A magnetic levitation device with two-dimensional movement, the so-called "levitating X-Y transporter," has been developed. In order to develop a working levitating X-Y transporter, it is necessary to clarify the levitation characteristics, such as the lift force, levitation height, and stability against mechanical disturbances. In this paper, we examine the lift and the restoring force experimentally and propose a new simulation program based on the three-dimensional hybrid finite and boundary element method to analyze the dynamic behavior of electromagnetic characteristics of YBCO bulk. Using the numerical simulation and experiments, we investigated a suitable arrangement of permanent magnets to enhance the levitation characteristics. We also designed a levitating transporter which can carry a load of 200 kg with a gap of 16 mm. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 44,54, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20220 [source] Research and Prospects of Iron-Based SuperconductorsADVANCED MATERIALS, Issue 45 2009Zhi-An Ren Abstract The discovery of a new superconductor, LaFeAsO1,xFx with a superconducting critical temperatureT,c, of 26,K in 2008, has quickly renewed interest in the exploration of iron-based superconductors. More than 70 new superconductors have been discovered within several months, with the highest Tc of up to 55,K being observed in the SmFeAsO1,x compound. High Tcs have previously only been observed in cuprates; these new iron-based superconductors have been added as second members of the high- Tc family. The crystal structure of these compounds contains an almost 2D Fe,As layer formed by FeAs4 tetrahedrons, which can be separated by an oxide or metal layer that provides extra electrons to the Fe,As layer, and the itinerant iron 3d electrons form an antiferromagnetic (AFM) order state in the undoped parent compounds at around 100,200,K. Superconductivity can be induced by carrier doping, which destroys the AFM ground state. In this Review, the most recent findings on and basic experimental facts about this class of high- Tc materials will be presented, including the various superconducting structures, the synthesis methods, the physical properties of the parent compounds, the doping methods that could produce superconductivity, pressure effects, and the prospects for this new iron-based high- Tc family. [source] | ||||||||||||||||||||||||||||||||||