Structure Of High-temperature Superconductors Research Articles

Simulation of the effect of peculiarities of the energy spectrum structure on the Hall coefficient behaviour in high- temperature superconductors

In this paper, we have investigated the influence of peculiarities of the normal-state energy spectrum structure in high-temperature superconductors on the temperature dependences of the Hall coefficient, RH. Methods for accounting different specific features of the charge-carrier system when approximating the differential Hall conductivity function were proposed and used for simulating the RH(T) dependences in the framework of a narrow-band model. Simulation results show the Hall coefficient to be most sensitive to the existence of an asymmetry of the dispersion law. Taking this property into account one can obtain the calculated RH(T) curves corresponding well to the experimental ones observed for samples of the Y-based system with different deviations from the stoichiometric composition. This finding corresponds well to results obtained previously when analyzing the Nernst coefficient behavior in the same system and should be used for a further development of the approach to the joint quantitative analysis of the normal-state electron transport in high-temperature superconductors.

Optimum Unit Sizing and Techno Economic Feasibility Investigation of Industrial Micro Grid

In this paper, we have studied the perovskite and cuprate crystallographic structure of high Tc super conductors. We know that the majority of single element crystal have highly symmetrical structure, generally fcc or bcc in which their physical properties are the same along the three crystallographic dimensions x, y and z. The NaCl type and A15 compounds are also cubic. Some compounds do have lower symmetric, showing that superconductivity is compitable with many different types of crystallographic structure, but higher symmetric are certainly more common. The structure of high temperature superconductors, almost all of which are tetragonal or orthorhombic. The structure plays very important role in determining the property of superconductors. The higher Tc is alloys of transitions metal are at the boundaries of resistibility between bcc and hep forms. Almost all the high-temperature oxide superconductors have point symmetry D4h ( a = b) or symmetry close to D4h ( a « b). These superconductors consists of horizontal layers, each of which contains one positive ion and either zero, one or two oxygen. The copper ions may be coordinated square planar, pyramidal, or octahedral, with some additional distortion. Copper oxide layers are never adjacent. The captions alternate sites vertically as do the oxygen. The copper oxide layers are either flat or slightly puckered, in contrast to the other metal oxide layers, which are generally far from planar. The highest Tc compounds have metal layers (e.g. Ca) with no oxygen between the Copper Oxide planes.

Angle-resolved photoemission studies on iron based high temperature superconductors

Copper oxide superconductors and iron-based superconductors are two important families of high temperature superconductors. Their high-temperature superconductivity mechanism is a long-standing issue and still in hot debate in the field of condensed matter physics. The extensive and in-depth exploration of iron-based superconductors and their comparative study with copper oxide high-temperature superconductors are of great significance for the development of new quantum theory, the solution of high-temperature superconducting mechanism, the exploration of new superconductors and practical applications of superconductors. The macroscopic properties of materials are determined by their microscopic electronic structure. Revealing the microscopic electronic structure of high temperature superconductors is fundamental for understanding high temperature superconductivity. Angle-resolved photoelectron spectroscopy, due to its unique simultaneous energy, momentum and even spin resolving ability, has become the most direct and powerful experimental tool for detecting the microscopic electronic structure of materials, and has played an important role in the study of iron-based high-temperature superconductors. The revealing and discovery of the Fermi surface topology, superconducting energy gap and its symmetry, three-dimensionality, orbital selectivity, and electronic coupling mode in different iron-based superconductor systems provide an important basis for identifying and proposing new theory of iron-based superconductivity to solve high temperature superconductivity mechanism.

Electrical resistance of SrFeO2 at ultra high pressure

SrFeO2 shows antiferromagnetic and insulating order at ambient pressure. The crystal structure of SrFeO2 has 2-dementional FeO2 plate and is interested in because this is common structure of high temperature superconductor. SrFeO2 has M-I, magnetic and spin transition with applying pressure. If magnetism disappears and metallization occurs with applying pressure, SrFeO2 may show superconductivity because of the crystal structure, so we measured electrical resistance at high pressure up to 150 GPa and low temperature down to 100 mK.

Hyperfine interactions of copper ions in the structure of high-temperature superconductors

Emission Mossbauer 61Cu(61Ni) spectra of simple MgO, NiO, Cu2O, CuO oxides and superconducting La2 − x Sr x CuO4, Nd2 − x Ce x CuO, and YBa2Cu3O7 − x copper metal oxides have been measured. It has been shown that emission Mossbauer spectroscopy on isotopes 61Cu(61Ni) makes it possible to determine the parameters of the electric gradient field tensor and magnetic field values in the copper sites of lattices of high-temperature superconductors and related materials.

Local Structure in Mg1−x Al x B2 System by High Resolution Neutron Diffraction

The local structure in high temperature superconductors is nowadays considered a key point for understanding superconductivity mechanism. MgB2 has a well-known simple structure; but its local structure remains quite unexplored. This is due to the fact that typical X-ray local probes, such as EXAFS, fail when used to study local structure of light atoms, such as Mg and B. We used high resolution neutron diffraction with pair distribution function (PDF) analysis for investigating disorder on the atomic scale in the Al doped Mg1−x Al x B2 system. The results indicate an anisotropic structural inhomogeneity along the c-axis that could be related with the delocalized metallic-type bonding between boron layers.

Peculiarities of REBCO Films Growth on Single Crystalline Substrates

ABSTRACTWe suggest a model of mismatched interface and calculate its energy in order to describe formation of threading edge dislocations by the mechanism of rotational relaxation of interface stresses. The model takes into account strongly layered perovskite structure of high-temperature superconductors. We have shown that rotational relaxation occurs due to finite size of clusters and to non-equilibrium effect of the film growth. We have predicted the subgrain size and the expected rotation of domains depending on the lattice mismatch. The computed values are consistent with the observed YBCO film nanostructure.

The Effect of the Crystal Structure of High-temperature Superconductors on the Superconducting Critical Temperature

The Effect of the Crystal Structure of High-temperature Superconductors on the Superconducting Critical Temperature

Charged vortex structure in high-temperature superconductors

By using a model Hamiltonian with competing antiferromagnetic (AFM) spin density wave (SDW) and d-wave superconductivity orders, the effect of next-nearest-neighbour (nnn) hopping on spin and charge structures in high-temperature superconductors is investigated at finite temperatures. For an optimally doped sample, we find that the AFM order magnitude in the vortex core is firstly enhanced and then suppressed, accompanied with a “positively → negatively → positively" charged vortex structure transition with increasing nnn hopping strength, which implies that the AFM order is unnecessarily bounded to an electron-rich vortex core. In addition, a charge ordering pattern with four negatively charged peaks localized in a small region is also found around the vortex core centre without net charge. Recent scanning-tunneling-microscopy experimental observations of the checkerboard structure are hopefully understood.

Energy structure of high-temperature superconductors with the intersite Coulomb interaction

The effect of the intersite Coulomb interaction of fermions on the ground state and energy structure of high-temperature superconductors is considered within the three-band Emery model using an extended basis of the irreducible operators orthogonal on Mori. The proposed theory allows prediction of bands of the fluctuation states whose spectral intensity grows with an increase in the root-mean-square fluctuations of the occupation numbers. The increase in these fluctuations in high-temperature superconductors upon doping plays a key role in redistribution of the integrated density of the Fermi states.

Momentum and Energy Dependence of the Anomalous High-Energy Dispersion in the Electronic Structure of High Temperature Superconductors

Using high-resolution angle-resolved photoemission spectroscopy we have studied the momentum and photon energy dependence of the anomalous high-energy dispersion, termed waterfalls, between the Fermi level and 1 eV binding energy in several high-T_{c} superconductors. We observe strong changes of the dispersion between different Brillouin zones and a strong dependence on the photon energy around 75 eV, which we associate with the resonant photoemission at the Cu3p-->3d_{x;{2}-y;{2}} edge. We conclude that the high-energy "waterfall" dispersion results from a strong suppression of the photoemission intensity at the center of the Brillouin zone due to matrix element effects and is, therefore, not an intrinsic feature of the spectral function. This indicates that the new high-energy scale in the electronic structure of cuprates derived from the waterfall-like dispersion may be incorrect.

About the role of 2D screening in high temperature superconductivity

The 2D screening is investigated in a simple single band square tight-binding model which qualitatively resembles the known electronic structure in high temperature superconductors. The Coulomb kernel for the two particle Bethe–Salpeter equation in the single loop (RPA) approximation for the polarization can be evaluated in a strong tight-binding limit. The results indicate an intense screening of the Coulomb repulsion between the particles, which becomes stronger and anisotropic when the Fermi level approaches half filling (or, equivalently, when the Fermi surface turns to be near the Van Hove singularities) and rapidly decreases away from it. The effect is also more pronounced for quasi-momenta regions near the corners of the Brillouin cell, which corresponds to dual spatial distances of the order of a few unit cells. Therefore, a possible mechanism is identified which could explain the existence of extremely small Cooper pairs in these materials, as bounded anisotropic composite particles joined by residual super-exchange or phonon interactions.

Vortex Lattice Structure of High Temperature Superconductors

We study vortex lattice structure of high temperature superconductors by using the Ginzburg–Landau model. The structure of the vortex lattice is oblique at the temperatures well below the transition temperature Tc, where the mixed s–d state is expected to have the lowest energy. Whereas, very close to Tc, the dx2-y2wave is slightly lower in energy, and a triangular vortex lattice recovers. The coexistence and the coupling between the s- and d-waves account for the upward curvature of the upper critical field curve HC2(T).

Filamentary model of vibronic spectra of YBa2Cu3O6.95

Ellipsometric synchrotron spectroscopy of YBCO provides persuasive evidence supporting the Phillips-Jung (PJ) filamentary nanodomain model of the electronic structure of high-temperature superconductors (HTSCs). The PJ model is part of a universal off-lattice topological platform that explains the origin of the intermediate phase that is responsible for high-temperature superconductivity, the stiffness transition and reversibility window in network glasses, and the folding transitions of proteins. In HTSCs it is both more specific and more general than descriptions based on conventional collective modes related to charge-density waves.

Relation of neutron incommensurability to electronic structure in high-temperature superconductors

The relation between the incommensurability observed in neutron scattering experiments in bilayer cuprate superconductors and the electronic structure is investigated. It is found that the observed incommensurability pattern, as well as its dependence on energy, can be well reproduced by electronic dispersions motivated by angle-resolved photoemission data. The commensurate resonance and its contribution to the superconducting condensation energy are discussed in the context of these calculations.

Andreev Bound-State Tunneling and ESR Spectroscopy of High-Temperature Superconductors and Observations of Broken Time-Reversal Symmetry

An emphasis on reliable materials growth and development of new fabrication techniques has allowed us to investigate the electronic structure of high-temperature superconductors by planar quasiparticle tunneling and electron paramagnetic resonance (EPR) spectroscopies. The quasiparticle (QP) density of states (DoS) is investigated by tunneling into oriented thin films of Y1Ba2Cu3O7 (YBCO) and single crystals of Ba2Sr2Ca1Cu2O8 (BSCCO). Data are obtained as a function of crystallographic orientation, temperature, doping, damage, and applied magnetic field. These data demonstrate that the observed zero-bias conductance peak (ZBCP) is composed of Andreev bound states (ABS) which intrinsically form at a symmetry-breaking interface of an unconventional superconductor, for example, a (110)-surface of d-wave YBCO. Tunneling into doped or ion-damaged YBCO provides a measure of the QP scattering rate below Tc. An applied field causes Doppler shift of the ABS, arising from the scalar product between the QP velocity and the superfluid momentum, vF·Ps, observed as a splitting in the ZBCP. Magnetic hysteresis of the splitting is consistent with the effects of strong vortex pinning near the interface. The directional field dependence shows that the ABS is highly anisotropic in its transport. These results, plus in-plane crystallographic orientational dependence on single-crystal BSCCO, demonstrate the d-wave symmetry of this superconductor. Below ∼ 8 K and in zero applied field, the ZBCP splits, indicating a transition into a superconducting state with spontaneously broken time-reversal symmetry (BTRS). EPR experiments are used to detect directly the spontaneous formation of the magnetic moments in the BTRS state.

Electronic structure studies of Bi 2 Sr 2 CaCu 2- x Sn x O 8+δ system

Photoemission measurements have been carried out for Bi2Sr2CaCu2-xSnxO8+? system with conventional x-ray photoemission spectroscopy for core-level spectra and synchrotron radiation photoemission spectroscopy for valence band. With Sn doping, all core levels shift differently in binding energy, and the intensity near fermi energy becomes smaller in valence band. From the experiment, we can deduce that the shifts of all core levels and valence bands may involve some other mechanisms, such as electrostatic effects, in addition to binding energy referencing effects. We argue that the chemical environment plays a crucial role in the electronic structure of high-temperature superconductors.

Strong electron correlation effects in X-ray and photoelectron spectra of high-temperature superconductors

This review is a detailed analysis of the literature (161 references) dealing with experimental and theoretical investigations of the electronic structure of high-temperature superconductors. Special attention is paid to the sudden perturbation model, which was effectively used to describe and interpret a series of X-ray and photoelectron experiments.

Electronic structure of high-temperature superconductors II. La-Ba-Cu-O systems

Electronic structure of La2−x Ba x CuO4 superconductors has been studied. Model systems La10CuO 22 −12 , La10cuO 14 +4 and LagBaCuO 14 +3 with various Ba positions have been investigated using the quasirelativistic INDO molecular orbital method. The oxidation state of copper atoms corresponds to Cu(II). The influence of Ba/La substitution on copper atoms is much lower than on their oxygen ligands sphere.

Are surface effects to be included in the study of the electronic structure of high temperature superconductors?

A first principles determination of surface effects on the electronic structure of Bi2201 is presented. We show that these effects will modify the Local Density Approximation (LDA) answer to the electronic structure of Bi2201 and thus should be considered if a comparison is made to surface sensitive experimental findings.