The Influence of Electron Transfer on Tc in Superconductors

Increase of Tc in Al1−x(SiO2)x cermets with increasing x is caused by electron transfer from the Al grains to the SiO2 phase occupying surface states, expressed by Tc/Tc,max=1−γ⋅n2(*), where n is the electron density in the Al phase and γa characteristic parameter. Decrease of Tc in Pb-Cu-sandwiches is attributed to the electron transfer from the Cu film to the Pb film. γand Tc,maxin equation (*) stands for the influence of the electron-phonon interaction and n2for the influence of the electron-electron Coulomb repulsion on Tc. The result that equation (*) holds for both hole-doped cuprate high-temperature superconductivity (HTSC) and Al1−x(SiO2)x cermets is an important indication that common mechanisms underlie HTSC and classical superconductors. The difference between the two is that in HTSC, electron transfer occurs between different electronic bands, but in Al1−x(SiO2)x cermets between different phases.

Single Crystal Growth and Physical Property Characterization of Non-centrosymmetric Superconductor PbTaSe_2

We report on the single crystal growth and superconducting properties of PbTaSe2 with the non-centrosymmetric crystal structure. By using the chemicM vapor transport technique, centimeter-size single crystals are success- fully obtained. The measurement of temperature dependence of electricaJ resistivity p（T） in both normal and superconducting states indicates a quasi-two-dimensional electronic state in contrast to that of polycrystalline samples. Specific heat C（T） measurement reveals a bulk superconductivity with Tc ≈ 3.75K and a specific heat jump ratio of 1.42. All these results are in agreement with a moderately electron-phonon coupled, type-g Bardeen-Cooper-Schrieffer superconductor.

Recrystallization Texture and Microstructure of Metal Substrate for Y123 Coated Superconductor

The cube textured pure Ni and non magnetic Cu Ni tapes were obtained by rolling and recrystallization, and these tapes are suitable as substrates of the second generation high temperature superconducting tape. The texture of tapes was studied using Orientation Distribution Function (ODF) and φ scans. The results indicate that sharp cube texture of Cu 0 70 Ni 0.30 and pure Ni was formed at 1000 ℃ and that of Cu 0 85 Ni 0.15 was formed at 900 ℃. The intensities of cube texture differ from each other. Uniform equiaxial crystallites are formed in all the tapes and the size of Cu 0.85 Ni 0.15 is larger than that of Cu 0.70 Ni 0.30 and pure Ni. Annealing twin is formed in Cu 0.85 Ni 0.15 and Cu 0.70 Ni 0.30 .

Explanation of Pressure Effect for High Temperature Superconductors Using Pressure Dependent Schrodinger Equation and String Theory

A pressure dependent Schrodinger equation is used to find the conditions that lead to superconductivity. When no pressure is exerted, the superconductor resistance vanishes beyond a critical temperature related to the repulsive force potential of the electron gass, where one assuming the electron total energy to be thermal, where applying mechanical pressure destroys Sc when it exceeds a certain critical value. However when the electron total energy is an assumed to be that of the free electron model and that the pressure is thermal and mechanical, the situation is different. The quantum expression for resistance shows that the increase of mechanical pressure increases the critical temperature. Such phenomenon is observed in high temperature cupper group.

THE MECHANISM OF ACCEPTING, DONATING AND EXCHANGING ELECTRONS IN SUPERCONDUCTOR

Based on ’Theoryof Electron Donating, Accepting and Exchanging’whichtheauthorpub lishedin 1989 ,thispaperexplainsin detailsaboutthesuperconductivityof metallicelements,metalliccompoundsand alloys. Italso providesa methodto raise Tc.

Design consideration of a super-high speed high temperature superconductor maglev evacuated tube transport (I)

The super-high speed high temperature superconductor （HTS） maglev evacuated tube transport （ETT） is a promising transport mode for the future. As a key component of the HTS maglev vehicle, the permanent magnet guide- ways （PMGs） with different geometrical configurations and iron yoke widths are analyzed by finite element method （FEM）. The levitation force of a single onboard HTS maglev device over the designed PMG at different field cooling heights （FCH） is measured by magnetic levitation measurement system. Based on the designed PMG and experimental results, a preliminary scheme of subterranean super-high speed HTS maglev ETT is described in this paper. The HTS maglev ETT is mainly composed of an evacuated tube, HTS maglev vehicle, PMG, propulsion system, station, emergency rescue system, etc. In addition, a subterranean tube that consists of foundation tube and vacuum airproof layer is introduced. In order to convert the stress caused by the air pressure difference between inside and outside of the vehicle, a multi-circular vehicle body is designed. The vehicle is driven by a linear motor propulsion system under the control of a ground controlling system. The scheme of long-distance super-high speed passenger transportation is accomplished by the connection of different vehicles.

A Study of Heavy-Fermion Superconductors via BCS Equations Incorporating Chemical Potential

Heavy-fermion superconductors (HFSCs) are regarded as outside the purview of BCS theory because it is usually constrained by the inequality , where EF, μ, kB, and θD are, respectively, the Fermi energy, chemical potential, Boltzmann constant, and the Debye temperature. We show that this restriction can be removed by incorporating μ into the equations for Tc and the gap Δ0 at T = 0. Further, when μ kBθD, we curtail the limits of the equations for Tc and Δ0 to avoid complex-valued solutions. The resulting equations are applied to a prominent member of the HFSC family, i.e., CeCoIn5, by appealing to ideas due to Born and Karmann, Suhl et al., and Bianconi et al. Since the equations now contain an additional variable μ, we find that 1) the Tc of the SC can be accounted for by a multitude of values of the (μ, λ) pair, λ being the interaction parameter;2) the λ vs. μ plot has a dome-like structure when μ kBθD;3) the (μ, λ) values obtained in 2) lead to reasonable results for the range of each of the following variables: Δ0, s, and n, where s is the ratio of the mass of a conduction electron and the free electron mass and n is the number density of charge carriers in the SC.

High T_c Superconductor Theoretical Models and Electromagnetic Flux Characteristics

High Tc Superconductors （HTS） have special electromagnetic characteristics and phenomena. Effort has been made in order to theoretically understand the appfied HTS superconductivity and HTS behaviors for practical appfications, various theoretical models related to the HTS electromagnetic properties have been developed. The theoretical models and analytic methods are summarized with regard to understanding the HTS magnetic flux characteristic which is one of the most critical issues related to HTS appfications such as for HTS magnetic levitation application.

Finite-difference time-domain studies of low-frequency stop band in superconductor-dielectric superlattice

The transmission coefficients of electromagnetic （EM） waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain （SO-FDTD） method is used in the analysis. By using the SO-FDTD method, the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers, from which a stop band starting from zero frequency can be apparently observed. The relation between this low-frequency stop band and relative temperature, and also the London penetration depth at a superconductor temperature of zero degree are discussed, separately. The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.

A 400 MHz Low Noise Amplifier at Cryogenic Temperature for Superconductor Filter System

A cryogenic low noise amplifier （LNA） using Agilent high electron mobility transistor （HEMT） for 380 MHzto 480 MHz is designed and fabricated, and the excellent cryogenic performance in superconducting receiver front-end for communication system is achieved. A special input impedance matching topology is implemented to provide low noise figure （NF） and good input matching in this cryogenic LNA design. The measurement results show that the NF is within 0.25 dB from the minimum NF of a single transistor, the power gain is above 20 dB, the flatness is within 1 dB, and the maximum input return loss is lower than -20 dB in bandwidth.

Combinatorial synthesis and high-throughput characterization of copper-oxide superconductors

Fast synthesis and screening of materials are vital to the advance of materials science and are an essential component of the Materials Genome Initiative. Here we use copper-oxide superconductors as an example to demonstrate the power of integrating combinatorial molecular beam epitaxy synthesis with high-throughput electric transport measurements. Leveraging this method, we have generated a phase diagram with more than 800 compositions in order to unravel the doping dependence of interface superconductivity. In another application of the same method, we have studied the superconductorto-insulator quantum phase transition with unprecedented accuracy in tuning the chemical doping level.

COMPOSITIONAL ANALYSIS OF HIGH-TEMPERATURE SUPERCONDUCTOR THIN FILMS BY HIGH ENERGY ELASTIC BACKSCATTERING OF HELIUM IONS

High energy ion backscattering can be used to enhance the sensitivity of oxygen analysis. At He++ ion energy of 8.8 MeV, the yield due to oxygen is about 25 times larger than that predicted by Rutherford formula. The elemental stoichiometry of some bulk and thin film superconductor samples was determined. The details of the measuring method are discribed.

The Holographic study for the high T_c superconductor YBCO and recent development of studies of a class of inverse problems

A dream or interesting problem is to obtain more information based on one measurement,for example to obtain all the thermodynamic functions based on specific heat only. We call it"holographic"study.After more than 10 year's efforts,we suggest one possibility(or only one)is to solve an inverse problem(specific heat-phonon spectrum inversion,SPI).In this talk we will review recent development of studies of a class of inverse problems,including Dai's exact solution and Chen's formula and their unification.T...

Preparation,Microstructure and Properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O Superconductor Tapes

The process to obtain high T(110K)phase quickly,the microstructure and properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconductor tapes have been studied.It was found that the formation time of the high T_c phase was greatly shortened by the addition of more Ca and Cu to the nominal composition of Bi(Pb):Sr :Ca:Cu=2:2:2:3 and the adoption of appropriate sintering temperature and cooling rate. Superconductor powder with predominant high T,phase was prepared after a 840 C/50 h treatment.The J of the Ag-sheathed tapes and the magnetic field dependence of Jwere obviously improved by repeatedly pres- sing and sintering.The maximum transport current density at 77K in a zero magnetic field was 12,200 A/cm^2. The magnetic dependence of Jwas summarized as follows:6.450 A/cm^(2)(B⊥1.B∥S.0.1T)1,810 A/cm^2 (B⊥1.B∥S,1T),390 A/cm^2(B⊥1.B∥S,2T)(B:magnetic field.1:electric current.S:surface of tapes).The improvement of Jwas attributed to the formation of the plate-like structure with homogeneous composition distribution and the strong c-axis texture.

A Study on Synthesis Kinetics of YBa_2Cu_3O_x High Tc Superconductor Powder

The synthesis kinetics of YBa_2Cu_30_x supercon- ductor was studied through comparing the calcina- tion (sintering) processes of different kinds of powders. It was shown that the temperature of synthesis of YBa_2Cu_30_x phase can be lowered from 950℃ to 800℃ through direct calcination of multiphase powder with uniform chemical com- position. The stress which is caused by the volume change during synthetic reaction breaks the particles. It facilitates the formation of highly active superfines of superconductor.

HIGH T_c SUPERCONDUCTOR YBa_2 Cu_3 O_x SYNTHESIZED BY UNIDIRECTIONAL REACTION

A unidirectional reaction for synthesis of the high T_c superconductor YBa_2Cu_3O_x has been proposed, Its T_c is 90-94.5 K and △T is 1 K. The phase relationships in the system Y_2BaCuO_5-Y_2Cu_2O_5-CuO-YBa_2Cu_3O_x were studied and discussed.

An Experimental Setup for Study of Photoresponse of High T_c Superconductors

We have developed an experimental setup that has been proven suitable for the study of photoresponse of high Tc superconductors. The distinguish feature of this experimental setup lies mainly in the data acquisition system which is equipped with computer as well as the IEEE-488 interface bus. which ensures the accuracy to experimental results. Using the experimental setup, the optical response to laser radiation in high-Tc superconductors has been examined, both of bolometric effect and nonequilibrium optical response are revealed.

Optimization of intergrain connection in high-temperature superconductor Bi_2Sr_2CaCu_2O_x

A modified spark plasma sintering（SPS） technique was developed for the fabrication of Bi2Sr2CaCu2Ox（Bi-2212）superconducting bulks with better intergrain connections. The influences of the modified SPS process on the microstructures, intergrain connections, and related superconducting properties were systematically analyzed. The modified SPS process can not only increase the final density of the bulk samples but also enhance the texture structures. Clean grain boundaries were obtained instead of the intergrain amorphous layers. Therefore the intergranular properties were obviously improved. Due to the better intergrain connections and the stronger flux pinning properties, the critical current densities of the Bi-2212 bulks obtained via the modified SPS process were greatly increased. The obtained improvements imply the possibility for the modified SPS technique to be used for enhancing the superconducting properties of the Bi-2212 tapes.