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Superconductivity
Kinds of Superconductivity Selected AbstractsResearch 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] Commercial Exploration of High-Temperature SuperconductivityLASER TECHNIK JOURNAL, Issue 4 2010Excimer Lasers Enable Novel Coated Superconductor Cylinders Superconductivity, which is the condition in which the electrical resistance of a material drops to zero, was discovered nearly 100 years ago. Since that time, large superconducting magnets such as those used in magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR) and big physics experiments have been developed and can now be regarded as being commercial products extending our capabilities in medicine and science. Yet many industrial applications of high temperature superconductivity (HTS) are on the horizon waiting to enter the marketplace. Currently, numerous manufacturers are working on improving and upscaling HTS materials, which operate at liquid nitrogen temperatures, and the most promising configuration for these materials is in the form of long tapes also known as coated conductors. These coated conductors are wound into coils in order to produce electrical components such as motors, magnets, transformers etc. Depending on the component to be made, there is an alternative to fabricating long unit lengths of superconducting tape, and in forming stable robust windings utilizing them. Now, a new technique has been developed which is using pulsed laser deposition (PLD) to deposit a series of layers of superconducting material directly on to the surface of a cylinder and patterning them into coils. This configuration provides a very direct route for the production of components that conventionally involve winding processes. This article explores how coated conductor cylinders can be produced utilizing this technique and explains why industriallyproven excimers represent the optimum choice of laser source for this emergingtechnology. [source] Reversible Optical Manipulation of Superconductivity,ANGEWANDTE CHEMIE, Issue 2 2010Aya Ikegami Bestrahlung mit Licht beeinflusst stark die Supraleitfähigkeit eines passivierten dünnen Nb-Films mit einer photochromen, selbstorganisierten Azobenzol(AZ)-Monoschicht (siehe Bild). Ursache sind Photoisomerisierungs-induzierte Veränderungen des Ausmaßes des Ladungstransfers zwischen Substrat und photochromer Monoschicht. Mit diesen Veränderungen geht ein Alternieren der Oberflächendipole einher. [source] Superconductivity of polymers with charge injection dopingANNALEN DER PHYSIK, Issue 12 2009A.N. Ionov Abstract We show that conductivity measurements on sandwiches of a polymer between normal-metal and superconducting-metal electrodes can be interpreted in terms of intrinsic superconductivity due to injection of charge into the polymer. [source] ChemInform Abstract: Unconventional Superconductivity in Ba0.6K0.4Fe2As2 from Inelastic Neutron Scattering.CHEMINFORM, Issue 11 2009A. D. Christianson 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: Magnetic Order Close to Superconductivity in the Iron-Based Layered LaO1-xFxFeAs Systems.CHEMINFORM, Issue 39 2008Clarina de la Cruz 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: Two-Band Superconductivity in LaFeAsO0.89F0.11 at Very High Magnetic Fields.CHEMINFORM, Issue 39 2008F. Hunte 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] Chemical Control of Electronic Structure and Superconductivity in Layered Borides and Borocarbides: Understanding the Absence of Superconductivity in LixBC.CHEMINFORM, Issue 45 2006Andrew M. Fogg 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] Unusual Lone Pairs in Tellurium and Their Relevance for SuperconductivityCHEMINFORM, Issue 14 2006Shuiquan Deng 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] Superconductivity of MRhGe2 (M: Zr, Hf).CHEMINFORM, Issue 23 2004M. Kasahi Abstract For Abstract see ChemInform Abstract in Full Text. [source] A Hidden Pseudogap under the "Dome" of Superconductivity in Electron-Doped High-Temperature Superconductors.CHEMINFORM, Issue 29 2003L. Alff Abstract For Abstract see ChemInform Abstract in Full Text. [source] Superconductivity in Two-Dimensional CoO2 Layers.CHEMINFORM, Issue 24 2003Kazunori Takada Abstract For Abstract see ChemInform Abstract in Full Text. [source] Single Crystal Growth, Bonding Analysis and Superconductivity of V2Ga5.CHEMINFORM, Issue 7 2003Kim C. Lobring Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: The Complex Nature of Superconductivity in MgB2 as Revealed by the Reduced Total Isotope Effect.CHEMINFORM, Issue 37 2001D. G. Hinks Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] Effect of Pb on the properties of Sr2YRu1-xCuxO6 crystals grown from PbO-PbF2 solutions at high temperaturesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2007S. M. Rao Abstract Single crystals of Sr2YRu1-xCuxO6 with x=0 and x=0.1 were grown using PbO-PbF2 based solutions at different temperatures in the range 1150,1350°C. The influence of Pb from the solutions and the Cu from the solid solutions of Sr2YRu1-xCuxO6 on the resulting crystals was studied using microstructure and magnetic property measurements. The peaks in the powder X-ray diffraction patterns and Raman spectra do not change in the case of x=0 crystals but shift in the presence of Cu. A diamagnetic transition indicative of superconductivity was observed in the presence of Cu and an antiferromagnetic behavior with x=0. Based on these results it is concluded that Pb may not be incorporated in the crystals and even if it does the influence is not observed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Diagrammatic Separation of Different Crystal Structures of A2BX4 Compounds Without Energy Minimization: A Pseudopotential Orbital Radii ApproachADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Xiuwen Zhang Abstract The A2BX4 family of compounds manifest a wide range of physical properties, including transparent conductivity, ferromagnetism, and superconductivity. A 98% successful diagrammatic separation of the 44 different crystal structures of 688 oxide A2BX4 compounds (96% for 266 oxide-only) is described by plotting the total radius of the A atom RA versus the radius of the B atom RB for many A2BX4 compounds of known structure types and seeking heuristically simple, straight boundaries in the RA versus RB plane that best separate the domains of different structure types. The radii are sums RA,=,Rs(A),+,Rp(A) of the quantum-mechanically calculated "orbital radii" Rs(Rp), rather than empirical radii or phenomenological electronegativity scales. These success rates using first-principles orbital radii uniformly exceed the success rates using classic radii. Such maps afford a quick guess of the crystal structure of a yet unmade A2BX4 compound by placing its atomic orbital radii on such maps and reading off its structure type. [source] High-Density Carrier Accumulation in ZnO Field-Effect Transistors Gated by Electric Double Layers of Ionic LiquidsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Hongtao Yuan Abstract Very recently, electric-field-induced superconductivity in an insulator was realized by tuning charge carrier to a high density level (1,×,1014 cm,2). To increase the maximum attainable carrier density for electrostatic tuning of electronic states in semiconductor field-effect transistors is a hot issue but a big challenge. Here, ultrahigh density carrier accumulation is reported, in particular at low temperature, in a ZnO field-effect transistor gated by electric double layers of ionic liquid (IL). This transistor, called an electric double layer transistor (EDLT), is found to exhibit very high transconductance and an ultrahigh carrier density in a fast, reversible, and reproducible manner. The room temperature capacitance of EDLTs is found to be as large as 34,µF cm,2, deduced from Hall-effect measurements, and is mainly responsible for the carrier density modulation in a very wide range. Importantly, the IL dielectric, with a supercooling property, is found to have charge-accumulation capability even at low temperatures, reaching an ultrahigh carrier density of 8×1014 cm,2 at 220,K and maintaining a density of 5.5×1014 cm,2 at 1.8,K. This high carrier density of EDLTs is of great importance not only in practical device applications but also in fundamental research; for example, in the search for novel electronic phenomena, such as superconductivity, in oxide systems. [source] Electronic and Magnetic Properties of SrTiO3/LaAlO3 Interfaces from First PrinciplesADVANCED MATERIALS, Issue 26-27 2010Hanghui Chen Abstract A number of intriguing properties emerge upon the formation of the epitaxial interface between the insulating oxides LaAlO3 and SrTiO3. These properties, which include a quasi two-dimensional conducting electron gas, low temperature superconductivity, and magnetism, are not present in the bulk materials, generating a great deal of interest in the fundamental physics of their origins. While it is generally accepted that the novel behavior arises as a result of a combination of electronic and atomic reconstructions and growth-induced defects, the complex interplay between these effects remains unclear. In this report, we review the progress that has been made towards unraveling the complete picture of the SrTiO3/LaAlO3 interface, focusing primarily on present ab initio theoretical work and its relation to the experimental data. In the process, we highlight some key unresolved issues and discuss how they might be addressed by future experimental and theoretical studies. [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] Self-Assembled Pb Nanostructures on Si(111) Surfaces: From Nanowires to NanoringsADVANCED MATERIALS, Issue 45 2009Rui Wu Abstract A template-directed growth method for metals is described in which ordered arrays of super-long single-crystalline metal nanowires with atomic-level-controlled width, thickness (height), and surface location are prepared by molecular beam epitaxy. Their subsequent examination by in situ scanning tunneling microscopy is also outlined. A phase-separated stripe pattern composed of alternately a Ge-rich incommensurate phase and a ,3,×,,3 phase is first obtained by Ge deposition on Si(111) substrates. Further deposition of Pb on this patterned surface leads to a well-ordered array of super-long Pb nanowires. Using the same mechanism, superconducting Pb nanorings can also be fabricated. In this review of our recent work, these Pb single-crystalline nanowires and nanorings are shown to serve as an ideal platform for the study of superconductivity in reduced dimensionalities. Furthermore, because the widths and spatial distributions of two phases can be precisely controlled by the Ge coverage and substrate temperature, and because a metal will always selectively nucleate on one of two phases, this template-directed growth method can be applied to a wide range of metals. [source] Madelung Strain in Cuprate Superconductors , A Route to Enhancement of the Critical TemperatureADVANCED MATERIALS, Issue 36 2009Vladimir Y. Butko "Madelung Strain" in cuprate films containing metal (M,=,La1.56Sr0.44CuO4) and insulator (I,=,La2CuO4) layers: X-ray diffraction shows that, unexpectedly, the volume of unit cell of the top layer adjusts to that of the bottom layer. The effect is due to long-range Coulomb forces; it affects interfacial superconductivity because the critical temperature scales with the unit-cell height. [source] Structure,Property Relation of SrTiO3/LaAlO3 InterfacesADVANCED MATERIALS, Issue 17 2009Mark Huijben Abstract A large variety of transport properties have been observed at the interface between the insulating oxides SrTiO3 and LaAlO3 such as insulation, 2D interface metallicity, 3D bulk metallicity, magnetic scattering, and superconductivity. The relation between the structure and the properties of the SrTiO3/LaAlO3 interface can be explained in a meaningful way by taking into account the relative contribution of three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. The emerging phase diagram is much richer than for related bulk oxides due to the occurrence of interface electronic reconstruction. The observation of this interface phenomenon is a display of recent advances in thin film deposition and characterization techniques, and provides an extension to the range of exceptional electronic properties of complex oxides. [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] Developments and Perspectives of Iron-based High-Temperature Superconductors,ADVANCED MATERIALS, Issue 19 2008Hai-Hu Wen Abstract Since the first report on superconductivity at 26,K in F-doped LaOFeAs at the end of February 2008, the superconducting transition temperature has been quickly raised to about 55,K and many new superconductors have been found, and superconductors with a higher condensing temperature are expected in this system. In this brief Research News article, the author will relate the enormous interest that has been generated towards new superconductor exploration, the refinement and tailoring of the single phase of the available superconductors, the growth of single crystals, and the theoretical and experimental efforts toward targeting the mechanism. Finally, a preliminary comparison between the iron-based system and the cuprates is given, as well as perspectives on these new iron-based superconductors. [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] Can the Fulleride superconducting model (FSM) be extended?INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005R. H. Squire Abstract The Fulleride superconducting model (FSM) is based on the existence of an electron (or Cooper) pair density wave localized on a single Fulleride molecule. Interaction of the wave with itinerant electrons at low temperature creates a pseudo-gap above the superconducting state. In addition, the interaction of the electron and the bosonic pair create a net attraction between two Fulleride molecules resulting in an intermolecular Cooper pair. This pairing interaction appears to have all the aspects of a spin liquid. This study extends the model to high-temperature superconductors and suggests that superconductivity may exist with considerably fewer molecules than in BCS theory. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Vibronic polarons: Self-trapping, local rotation, and band featuresINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2002A. G. Andreev Abstract We revisit basic theoretical concepts of local and itinerant vibronic polarons in crystals. The following results may be regarded as novel: (1) The electron self-trapping rate to a small polaron is calculated via the reaction rate method; subsequently, self-trapped on-center small polarons relax to an off-center vibronic polaron state. (2) The general vibronic Hamiltonian is redefined so as to incorporate both local and itinerant behavior and pairing into bipolarons or Cooper pairs. (3) The planar rotation and diametral tunneling of an off-center polaron around and across its centrosymmetrical site are dealt with to adiabatic approximation. (4) Variational calculations are made for vibronic polarons itinerant along 1-D chains by means of a two-band extension of Merrifield's ansatz. This investigation of vibronic polarons is undertaken in view of their presumed role in high-temperature superconductivity and colossal magnetoresistance. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [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] Commercial Exploration of High-Temperature SuperconductivityLASER TECHNIK JOURNAL, Issue 4 2010Excimer Lasers Enable Novel Coated Superconductor Cylinders Superconductivity, which is the condition in which the electrical resistance of a material drops to zero, was discovered nearly 100 years ago. Since that time, large superconducting magnets such as those used in magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR) and big physics experiments have been developed and can now be regarded as being commercial products extending our capabilities in medicine and science. Yet many industrial applications of high temperature superconductivity (HTS) are on the horizon waiting to enter the marketplace. Currently, numerous manufacturers are working on improving and upscaling HTS materials, which operate at liquid nitrogen temperatures, and the most promising configuration for these materials is in the form of long tapes also known as coated conductors. These coated conductors are wound into coils in order to produce electrical components such as motors, magnets, transformers etc. Depending on the component to be made, there is an alternative to fabricating long unit lengths of superconducting tape, and in forming stable robust windings utilizing them. Now, a new technique has been developed which is using pulsed laser deposition (PLD) to deposit a series of layers of superconducting material directly on to the surface of a cylinder and patterning them into coils. This configuration provides a very direct route for the production of components that conventionally involve winding processes. This article explores how coated conductor cylinders can be produced utilizing this technique and explains why industriallyproven excimers represent the optimum choice of laser source for this emergingtechnology. [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] | |||||||||||||||||||||||||||||||