Discovery Of high-Tc Superconductors Research Articles

Bound-electron pairs within a repulsive Hubbard model in two-coupled linear chains

The study of electronic correlation in multiple layer materials provides an opportunity to understand the different pairing mechanism, their importance can be traced to the discovery of high Tc superconductors, superconductivity for a magic-angle in graphene lattices and others. In this work, we analyzed the two-interacting fermions in two-coupled periodic chains (ladder) within an attractive or repulsive potential, we obtain an analytical solution using the real-space mapping method. This real-space method is based on mapping the correlated many-body problem onto an equivalent tight-binding problem in a higher dimensional space. With this in mind, our ladder problem maps into a one-particle four dimensional lattice, which finally can be projected into an effective lattice of states in three dimensions. Two kind of solutions have been found, the antisymmetrical solution, which reduce the problem to two independent linear chains (one without impurities and the other with a central impurity) and the symmetrical solution corresponding to a ladder with an impurity. The latter solution is quite interesting since it allow us also to observe the new bound-electron pairs for E<0 in a repulsive potential (U>0).

Record high Tc element superconductivity achieved in titanium

It is challenging to search for high Tc superconductivity (SC) in transition metal elements wherein d electrons are usually not favored by conventional BCS theory. Here we report experimental discovery of surprising SC up to 310 GPa with Tc above 20 K in wide pressure range from 108 GPa to 240 GPa in titanium. The maximum Tconset above 26.2 K and zero resistance Tczero of 21 K are record high values hitherto achieved among element superconductors. The Hc2(0) is estimated to be ∼32 Tesla with coherence length 32 Å. The results show strong s-d transfer and d band dominance, indicating correlation driven contributions to high Tc SC in dense titanium. This finding is in sharp contrast to the theoretical predications based on pristine electron-phonon coupling scenario. The study opens a fresh promising avenue for rational design and discovery of high Tc superconductors among simple materials via pressure tuned unconventional mechanism.

小型NMR 用円筒状超伝導バルク磁石の開発と信号検出

The discovery of high Tc superconductors has led to the development of novel applications of bulk materials for practical industries, as well to the application of the wiring for metallic low-temperature superconductors. Uniform REBCO bulk materials have been successfully manufactured with the size reaching more than 60 mm in diameter, and these cylindrical superconducting bulk magnets have created applications for compact cryogen-free NMR magnets. In the latest research, a newly designed magnet composed of eight-stacked bulk magnets has been developed. Furthermore, a GdBCO tape was wound around the copper pipe, and this was inserted into the bore of the magnet. The NMR spectrum resolution of 1 Hz at the full width at half maximum was observed on this magnet. This proved that the magnetic field homogeneity required for the high-resolution NMR has been accomplished using a cylindrical superconducting bulk magnet. In the near future, the mechanical strength of the bulk superconductor itself will be improved, leading to the common use of 400 MHz (9.4 T) NMR magnets.

Recent Progress in the Superconductivity Research Field -Application of Superconducting Tapes and Discovery of New Materials-

Major developments in the research field of superconductivity have been achieved in 2008. Since the discovery of high-Tc superconductors, their practical application has been studied by many researchers. Coated conductors consisting of an YBa2Cu3Oy superconducting layer deposited on metal tapes buffered oxide layers were developed in the NEDO project between FY2003 and FY2007. These technologies for coated conductors are expected to be applicable to electrical power equipment. A new NEDO project that started in FY2008 is focusing on the development of superconducting electric power equipment such as power cables, superconducting magnetic energy storage devices (SMES) and transformers. Furthermore, a new family of high-Tc superconductors, Fe-As-O-based superconductors, has been discovered. The highest reported critical temperature, Tc, has rapidly increased owing to the considerable effort of many researchers. A new social environment based on superconductivity technology might indeed be realized in the near future.

Chemistry and electronics of oxides from carbon dioxide to perovskite

Oxides are thermodynamic stable form of materials in terrestrial conditions to exist as final products of energy consumption proceeding in nature as well as in civilization. The accumulation of heat capacitive CO 2 in atmosphere is becoming a serious environmental problem. Solid oxides as minerals in the earth shell had been used mainly for heat resistant structural materials as well as for raw materials of metals, but recent advanced chemistry and physics have been manifesting new electronic and chemical potentials hidden in oxides. Current interest and studies on oxides are directed towards two main areas: (1) prevention of CO 2 increase in atmosphere by its fixation and/or by saving the consumption of fossil fuels and (2) discovery and utilization of superfunctionality in oxides. Triggered by Bednorz and Muller's discovery of high Tc superconductor, the latter topics have been attracting rapidly growing interest from viewpoints of both fundamental research and practical application. In commemoration of WOE homecoming to the place of inauguration, a founder of WOE appreciates much to the program committee for providing him with this opportunity of briefing the workshop motivation and of reviewing his research career on oxide materials.

Advances in Bi-Based High-Tc Superconducting Tapes and Wires

Since the discovery of high-Tc superconductors (HTSs), especially the Bi-based oxide superconductors (Bi-HTSs) in 1989, much effort has been concentrated on the fabrication of Bi-HTS wires and tapes. Bi-HTSs are interesting materials from the viewpoint of practical applications. One of the interesting applications of Bi-HTSs is the cryogen-free conduction-cooled magnet. Besides having a high transition tem- perature (Tc), Bi-HTSs have high upper critical fields (Bc2) or high irreversibility fields (Birr) at temperatures below ∼30 K. Because ∼30 K can be efficiently main- tained by a cryocooler, a Bi-HTS magnet cooled with a cryocooler has great potential in many technological applications. Another promising application of Bi-HTSs is the high-field magnet. When the temperature is reduced to ∼5 K, Bi-HTSs show a much higher Bc2 or Birr than do conventional metallic superconductors (low-temperature superconductors, LTSs) such as Nb3Sn. This indicates that Bi-HTSs also have great potential for use in a high- field superconducting magnet if the magnet is operated at low temperature.

THE DYNAMIC MECHANICAL PROPERTIES OF YBCO SUPERCONDUCTOR

Since the discovery of high Tc superconductors, the studies of mechanical properties of superconductors have been developed. In 1987, R.F. Cook et al. measured the fracture toughness on single crystals1 and polycrystalline2 YBCO. The bulk modulus, Young's modulus, strength and microhardness had been measured by many authors. 3,5 The mechanical properties of high Tc superconductors are of interest because their usefulness in bulk form hinges on their ability to withstand not only the forming operations but also many stresses (such as those caused by coil winding, thermal contraction, and the Lorentz force generated by magnetic field) imposed during use.

Low field ultrasonic studies on melt-textured YBa2Cu3O7−δ

Ultrasonic attenuation and velocity measurements have proved to be a useful probe for the study of conventional superconductors, where the electron–phonon coupling is the dominant pairing mechanism. Since the discovery of high Tc superconductors, ultrasonic measurements have been performed on these systems with moderate success. In the absence of large single crystals, measurements have been performed on isotropic sintered pellets and partially oriented sintered pellets of these high Tc compounds. Low field ultrasonic measurements in the melt textured YBa2Cu3O7 have proved to be interesting. With shear waves one can see a coupling of the sound waves to the flux lattice. As the field is increased, there is an abrupt jump in both the sound velocity (ΔV) and the attenuation (Δα) at a field Hc1’, which is close to Hc1. The temperature dependence of Hc1’ is the same as that of Hc1. ΔV is found to be proportional to the square root of Hcl’, that is inversely to the average distance between the flux lines. Δα goes to zero at Tc and at T=0, going through a maximum at ∼55 K. Measurements have been done for various orientations of the magnetic field. As no anisotropy is seen in the value of Hc1’, it is surmised that Hc1’ is the lower critical field for the intergranular matrix. [Work supported by ONR.]

Communication between Chinese and non-Chinese scientists in the discovery of high-Tc superconductor: I. The formal perspective

Data obtained through letter poll over 143 researchers who authored the 240 highly cited documents (See the first phase of the study) were used to describe the informal aspects of communication between Chinese and non-Chinese superconductivity researchers. While non-Chinese researchers played both roles equally, Chinese scientists were the destination more often than they were the source in informal communication. Chinese scientists were less visible than their counterparts in the informal domain. The mapping of the informal communication activities among the superconductivity researchers shows that all Chinese scientists except Zhao ZX, a special liaison between the two groups of researchers, clustered away from their non-Chinese colleagues.

Communication between Chinese and non-Chinese scientists in the discovery of high-Tc superconductors: II. The informal perspective

Communication between Chinese and non-Chinese scientists in the discovery of high-Tc superconductors: II. The informal perspective