Intensive study of the HIGH TEMPERATURE SUPERCONDUCTORS has been ongoing for two decades. A great deal of this effort has been devoted to the underdoped regime, where the new and difficult physics of the doped Mott insulator has met   extra complications including bilayer coupling/splitting, shadow bands, and hot spots. While these complications continue to unfold, in this short overview the focus is moved to the region of actual HIGH-Tc, that of optimal doping. The focus here also is not on the superconducting state itself, but primarily on the characteristics of the normal state from which the superconducting instability arises, and even these can be given only a broad-brush description. A reminder is given of two issues: (i) why the “optimal Tc” varies: for n-layered systems it increases for n up to 3, then decreases; for a given n, Tc increases according to the ‘basis’ atom in the order Bi, Tl, Hg; (ii) how does pressure, or a particular uniaxial strain, increase Tc when the zero-strain system is already optimally doped?

We explore the important role of the strong electron-phonon interaction in HIGH TEMPERATURE superconductivity through the study of the results of some important experiments, such as inelastic neutron and X-ray scattering, angle resolved photoemission spectroscopy, and isotope effects. We also present our computational results of the eigenvalues and eigenvectors of the Ag Raman modes, and the ionic displacement dependence of the electronic band structure by density functional theory. It is clearly evident that the role of phonons in the mechanism behind the HIGH-TEMPERATURE superconducting state should be seriously considered.

Neutron scattering is proved to be a vital probe in unveiling the magnetic properties of HIGH TEMPERATURE SUPERCONDUCTORS (HTSC). Detailed information about the energy and momentum dependence of the magnetic dynamics of HTSC have been obtained directly by this technique. Over the past decade by improving the crystal growth methods, large and HIGH quality single crystals of HTSC, which are essential for a neutron scattering experiment, have become available. The results of neutron scattering measurements on such crystals have considerably enhanced our understanding of the magnetism in HTSC both in the superconducting (SC) and normal states. In this review, the neutron scattering results on two main HTSC families, La2-xSrxCuO4 (LSCOx) and YBa2CuO3O6+x (YBCO6+x), are considered with an emphasis on the most prominent properties of these materials that are now widely accepted. These include the presence of strong antiferromagnetic (AF) fluctuations even in optimally doped region of the phase diagram, neutron resonance peak that scales with SC transition TEMPERATURE, Tc, incommensurate magnetic fluctuations (stripes), and a pseudogap in the normal state of underdoped materials.

Superconducting materials are capable of trapping extremely HIGH magnetic fields. This property and Meissner effect of SUPERCONDUCTORS causes a levitation force between bulk SUPERCONDUCTORS and a permanent magnet (PM). This levitation force has possible industrial applications such as Permanent Magnet Guideways (PMG). Because of the HIGH price of permanent magnets, the optimization of PMG design is necessary and beneficial. A heuristic optimization method has been proposed for the optimum arrangement and dimensions of permanent magnets in different structures of PMGs, which guarantee the satisfactory levitation performance. Therefore, finite element simulation, based on the estimation of penetration depth and self-inductance of the superconductor disk, has been utilized. The variation of the PMG features, such as its dimensions and cost versus the system parameters, such as the levitation height and the superconductor disk characteristics have been presented as the optimization results. Based on the optimization process outputs, PMG prototypes have been fabricated and tested successfully.

The Bit17Sb0.3Sr1.97Ca2.03Cu3.1 Oy SUPERCONDUCTORS are prepared by sol-gel method and the effect of W03 and MnO2 additives on their properties are studied. Structural studies show that the find samples are homogeneous and are mainly composed of 2223 and lower percents of 2212 phases. Analysis of the X-ray diffraction patterns indicate that the penetration of W6+ ions into superconducting phase considerably increases for more than 2 wt% additives. Also, the penetrating W6+ions preferentially occupy 4e and 2a crystallographic sites of Cu atoms. The electrical measurements show that the best superconducting properties obtain for the sample with 1 wt% of WO3 additive, while superconductivity is weakened for HIGHer amounts of WO3. For the sample with 0.5 wt% of MnO2 additive, the best superconducting properties are obtained after sintering at 830°C.

In this study, the effect of of silver nanoparticles (Ag-NPs) inclusion on the AC magnetic susceptibility of HIGH TEMPERATURE YBa2Cu3O7-δ,(Y123) + x wt% Ag (x=0. 00, 0. 06, 0. 10 and 0. 30) polycrystalline SUPERCONDUCTORS was investigated. The HIGH TEMPERATURE SUPERCONDUCTORS (Y123 + x wt% Ag) were fabricated by the solid state reaction method. XRD analysis of the samples showed superconducting orthorhombic phase with symmetry of Pmmm space group. Analysis of scanning electron microscopy (SEM) images related to the surface morphology of the samples showed that increasing silver nanoparticles dopant causes a decrease in granule size of the compounds. Real magnetic susceptibility exhibited intrinsic diamagnetic behavior and grain boundary connections and imaginary components of magnetic susceptibility showed energy loss due to flux penetration and vortex movement at the grain boundary. The critical TEMPERATURE of 92 K was obtained for pure Y123 by real component of magnetic susceptibility and complete diamagnetism was observed in all samples (x=0. 00, 0. 06, 0. 10 and 0. 30). Silver decreased the critical TEMPERATURE and increased the critical current density. Based on the obtained values of maximum Josephson current and Josephson intergranular energy coupling, it can be concluded that x=0. 10 is the best weight percentage for Ag among the Y123 doped samples. Indeed, the greater inter-granular Josephson coupling energy causes, the superior of the trapping force and consequently produces the better critical current density.

In the quest for understanding correlated electrons, HIGH-TEMPERATURE superconductivity remains a formidable challenge and a source of insight. This paper briefly recalls the central achievement by the study of heat transport at low TEMPERATUREs. At very low TEMPERATUREs, nodal quasi-particles of the d-wave superconducting gap become the main carriers of heat. Their thermal conductivity is unaffected by disorder and reflects the fine structure of the superconducting gap. This finding had led to new openings in the exploration of other unconventional SUPERCONDUCTORS.

A systematic study of the intergranular properties of (Bi,Pb)2 Sr2Ca2CU3Oy (Bi2223) polycrystalline samples has been done using the electrical resistivity and AC susceptibility techniques. In this study, we have prepared a series of Bi2223 samples with different sintering TEMPERATUREs. The XRD results show that by increasing the sintering TEMPERATURE up to 865°C, the Bi2212 phase fraction decreases. It was found that the Bi2212 phase on the grain boundaries is likely to play the role of the weak links and consequently reduces the intergranular critical current densities.

Bi1.8Pb0.4Sr2-xBaxCa2.2Cu3Oy (x-0, 0.1, 0.2, 0.3) samples were prepared by a conventional solid state reaction method. The effect of Ba substitution at Sr site in Bi-2223 HIGH-TC SUPERCONDUCTORS have been investigated by the XRD, SEM, dc electrical resistivity and ac susceptibility. XRD and SEM analysis indicated Ba substitution decreased TEMPERATURE of 2223 phase formation. The HIGHest 2223 phase fraction was obtained for the sample with x=0.1 (A1 sample). This phase decreased by increasing Ba concentration (x>0.1). Ba doping up to x=0.1 decreased impurity phases but doping more than 0.1 increased. Dc electrical resistivity data and ac susceptibility measurements showed the transition TEMPERATURE of grains and grain boundaries (Tc, Tcj) increased and the transition width (DTc) decreased for A1 sample. This behavior can be described by decreasing impurity phases and increasing 2223 phase. Flux pinning force and intergranular critical current densities (Jcm) of A1 sample increased. It was suggested it is because of a small precipitation of Ba in grain boundaries as effective pinning centers. Ba doping more than 0.1 reduced the intergranular coupling and increased weak link behavior by increasing impurity phases. It decreased Tcj, Jcm and flux pinning force.

We have investigated the effect of Niobium and Nano CuO (40 nm) dopingY1-xNbxBa2Cu3O7-∂ compounds with 0.00 ≤ x ≤ 0.05 wt. %, prepared by the conventional solid-state method by means of XRD, SEM, R(T) and magnetic loops (M-H) measurements. The critical current densities, Jc as a function of TEMPERATURE have been calculated using the critical state model from the hysteresis loops up to 1 kG at the TEMPERATURE range of 10-60 K. Magnetic flux pinning, Fp of samples was calculated by using Lorentz force. The TEMPERATURE dependence of the electrical resistivity measurement curves indicated that the sample with x=0.01 wt.% has a HIGH transition TEMPERATURE, Tc. XRD analysis shows a shorter c axis lattice parameter and HIGHer orthoromthcity than the pure Y-123 and other Nb-doped samples. It was also found from Jc and Fp measurement, that the 0.01 wt.% Nb substation for the Y on YBCO superconductor improves the Jc and Fp.