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The presence of nano-structures, i.e. static or dynamic stripe-like features or nano-domains in HTSC, can cause a quasi-1D flow of a transport current through these materials. We present the experimental results, which reveal the effect of a filamentary flow of the current on the normal and superconducting transport properties of HTSC.

For high–T_c superconductor metal oxides (HTSC) it is shown that the dc resistivity and Hall effect temperature behaviour can be explained by the model of the paraelectric material close to the point of the Mott-Hubbard instability, in the ground state of which the current is carried by a liquid of boson-like pairs of carriers in upper and lower Hubbard bands. The Mott-Hubbard instability corresponds to the order-of-lattice-constant length of the mean free path and results in the temperature insensitivity of Drude conductivity. Nearly linear on T resistivity results from the Curie law via the local (acting) electric field. Fermion-like carriers, temperature excited over the energy of boson-like pair dissociation (pseudo gap), explain the temperature behaviour of Hall effect. Available data are compared with the model.

High pressure-high temperature electrical resistivity study on composition-controlled Nd_0.9Ca_0.1Ba₂Cu₃O_7-δ high T_c superconductor (HTSC) is carried out by a four-probe technique using Bridgman anvils. A simple heating coil arrangement is used for heating the samples. Electrical resistivity behavior under pressure (up to a maximum of 8 GPa) at various temperatures (up to a maximum of 523 K) were studied and reported in this paper. Simulation of energy dispersive X-ray diffraction confirms substitution of calcium at the Nd site of Nd-123. Variation of the electrical resistivity under pressure is compared with that of the structural changes and the bulk modulus was determined.

Recent STM studies revealed nanoscale electronic disorder on the crystal surface in many cuprates. In BSCCO strong correlations between oxygen defect distributions on its surface and both the gap map and the coherence peak amplitude showed that the off-center distortions in the positions of oxygen atoms are responsible for most of the electronic disorder. Additional information on nanoscale inhomogeneities and its relationship to the lattice strain and oxygen redistribution can be obtained from the electrical transport that uses Percolating Persistent Supercurrents which are known to bypass regions of a reduced order parameter (macroscopic crystal defects). Our investigations identified universal (sample independent) features in the superconducting properties which can be attributed to the presence of a nanoscale inhomogeneity, such as nanogranular Josephson effects, strain-induced filamentary and percolative flow of the transport current, etc. Local oxygen redistribution, induced either by careful low temperature annealing or by room temperature aging, modifies both the superconducting and the normal state properties.

Numerical electromagnetic field simulations of high-temperature superconductors (HTSC) bulk were carried out to calculate the magnetic force between the HTSC bulk and the permanent magnet railway (PMR). A 3D-modeling numerical calculation method is proposed using the finite element method. The model is formulated with the magnetic field vector (H-method). The resulting code was written with FORTRAN language. The electric field intensity E and the current density J constitutive relation of HTSC were described with E–J power law. The Kim macro-model is used to describe critical current density J_c of HTSC bulk. Two virtual HTSC bulks were used to solve the critical current density J_c anisotropic properties of HTSC materials. A superconducting levitation system composed of one HTSC bulk and PMR is successfully investigated using the proposed method. By this method, the influence of critical current density on magnetic levitation force of the superconducting levitation system is mathematically studied.

Former results for a tight-binding (TB) model of CuO planes in La₂CuO₄ are reinterpreted here to underline their wider implications. It is noted that physical systems being appropriately described by the TB model can exhibit the main strongly correlated electron system (SCES) properties, when they are solved in the HF approximation, by also allowing crystal symmetry breaking effects and noncollinear spin orientations of the HF orbitals. It is argued how a simple 2D square lattice system of Coulomb interacting electrons can exhibit insulator gaps and pseudogap states, and quantum phase transitions as illustrated by the mentioned former works. A discussion is also presented here indicating the possibility of attaining room temperature superconductivity, by means of a surface coating with water molecules of cleaved planes of graphite, being orthogonal to its c-axis. The possibility that 2D arrays of quantum dots can give rise to the same effect is also proposed to consideration. The analysis also furnishes theoretical insight to solve the Mott–Slater debate, at least for the La₂CuO₄ and TMO band structures. The idea is to apply a properly noncollinear GW scheme to the electronic structure calculation of these materials. The fact is that the GW approach can be viewed as a HF procedure in which the screening polarization is also determined. This directly indicates the possibility of predicting the assumed dielectric constant in the previous works. Thus, the results seem to identify that the main correlation properties in these materials are determined by screening. Finally, the conclusions also seem to be of help for the description of the experimental observations of metal-insulator transitions and Mott properties in atoms trapped in planar photonic lattices.

The pseudogap effects and the expected quantum phase transitions (QPTs) in cuprate materials are yet unclear in nature. A single band tight-binding (TB) model for the CuO₂ planes of these materials had predicted the existence of definite pseudogap states at half-filling, after considering that a crystal symmetry breaking and noncollinear spin orientations of the single particle states are allowed. Here we show that after including hole doping in the model, a QPT which lies beneath the superconducting dome exists and is a second-order one. In it, an antiferromagntic-insulator (AFI) ground state, showing strong spin fluctuations at low doping, coalesce with an excited paramagnetic pseudogap (PPG) state, exhibiting a broken lattice symmetry at the critical hole density. A critical doping value x_c = 0.2 resulted, which surprisingly coincided with the experimentally measured one, in spite of the fact that the model parameters were not yet optimized. Above this value the system becomes a paramagnetic metal. The band structures and Fermi surface with doping are evaluated and their evolution show a close resemblance with the experimental observations, including the topological change in structure at the critical hole density.

In this paper, the magnetic fields end-face effect of high temperature superconducting (HTS) bulk over a permanent magnetic guideway (PMG) is researched with 3D-modeling numerical method. The electromagnetic behavior of the bulk is simulated using finite element method (FEM). The framework is formulated by the magnetic field vector method (H-method). A superconducting levitation system composed of one rectangular HTS bulk and one infinite long PMG is successfully investigated using the proposed method. The simulation results show that for finite geometrical HTS bulk, even the applied magnetic field is only distributed in $x$–$y$ plane, the magnetic field component Hz which is along the $z$-axis can be observed interior the HTS bulk.

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In this paper, we investigate the temperature dependence of the transverse conductivity in Y_1-zPr_zBa₂Cu₃O_7-δ single crystals with different praseodymium concentrations. It is determined that the increase of the praseodymium concentration in Y_1-zPr_zBa₂Cu₃O_7-δ leads to the enhancement of localization effects. This in turn results to the transition from the pseudo-gap regime to the variable-range-hopping regime.