Nernst Signal in High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

The time-dependent Ginzburg–Landau equation with thermal noise is used to calculate the Nernst signal e _N , describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The Gaussian method used is an elaboration of the Hartree–Fock method. An additional assumption often made in analytical calculations that only the lowest Landau level significantly contributes to physical quantities of interest in the high-field limit is lifted by including all the Landau levels. The values of e _N are in good quantitative agreement with experimental data for temperature close to T _c on Bi₂Sr₂CaCu₂O_8+δ and Bi₂Sr₂Ca₂Cu₃O_10+δ .     

Spin Dynamics in the Bi-Directional Charge Density Wave State of High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

In this paper, we investigate the dynamical spin susceptibility in the bi-directional charge density wave (BCDW) state by adopting a random-phase approximation. In the BCDW state, we find that no spin resonance exists and only a broad commensurate peak appears for the frequency dependence of the dynamical spin susceptibility at Q = (π,π), though a low-energy spin gap feature can also be found as in the superconducting state. While the “hourglass” type of the dispersion for the BCDW state bears some similarities with that in the superconducting state, the momentum distribution of Im χ ^+?(Q,ω) is just the opposite with the incommensurate peaks lying along the diagonal direction for the energy below ω _c and along the axial direction above ω _c . In the coexistence of SC and BCDW, the frequency dependence of the dynamical spin susceptibility at Q = (π,π) generally shows the two-peak structure, reflecting two energy scales of the spin excitations. These unique features may serve as signatures to verify whether or not the BCDW state is responsible for the formation of the Fermi arcs.     

Magnetic Brake Considerations for the High-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> Superconducting Maglev Vehicle System

Levitation, guidance and driving/braking are three indispensable parts for a high temperature superconducting Maglev vehicle system. To maintain the advantage of a passive, non-contact levitation system, a magnetic brake based on a discontinuous permanent magnet guideway (PMG) is introduced. Its feasibility is verified by the experimental investigations on the behavior of a levitated bulk high temperature superconductor (HTSC) moving towards the broken-off PMG. When the bulk moves towards the broken-off PMG, a braking force will be generated to hold back the bulk due to the inhomogeneous field distribution. That is to say, this magnetic braking mechanism can act as a safe-protection function. The magnetic brake just makes use of the existing PMG, which is very simple with no extra components needing to be added. This makes it very economical and practical for the future application of the HTS Maglev vehicle system.     

Novel Solid-State Growth of <Emphasis Type="Italic">p</Emphasis>-Terphenyl: the Parent High-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> Organic Superconductor (HTOS)

We report an easy and versatile route for the synthesis of the parent phase of the newest superconducting wonder material, i.e., p-terphenyl. Doped p-terphenyl has recently shown superconductivity with transition temperature as high as 120 K. For crystal growth, the commercially available p-terphenyl powder is pelletized, encapsulated in an evacuated (10^?4 Torr) quartz tube and subjected to high-temperature (260 ^°C) melt followed by slow cooling at 5 ^°C/h. A simple temperature-controlled heating furnace is used during the process. The obtained crystal is one piece, shiny, and plate like. Single crystal surface XRD (X-ray diffraction) showed unidirectional (00l) lines, indicating that the crystal is grown along the c-direction. Powder XRD of the specimen showed that as grown p-terphenyl is crystallized in monoclinic structure with space group P2 ₁/a space group, having lattice parameters a = 7.672 (2) Å, b = 5.772 (5) Å, and c = 13.526(3) Å and β = 91.484 (3)^°. Scanning electron microscopy (SEM) pictures of the crystal showed clear layered slab-like growth without any visible contamination from oxygen. Characteristic reported Raman active modes related to C–C–C bending, C–H bending, C–C stretching, and C–H stretching vibrations are seen clearly for the studied p-terphenyl crystal. The physical properties of the crystal are yet underway. The short letter reports an easy and versatile crystal growth method for obtaining quality p-terphenyl. The same growth method may probably be applied to doped p-terphenyl and to subsequently achieve superconductivity to the tune of as high 120 K for the newest superconductivity wonder, i.e., high- T _c organic superconductor (HTOS).     

Simulation Study of Noise Effect on Shapiro Steps in High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Josephson Junctions Using RCLSJ Model

The current voltage characteristics of Josephson junctions at finite temperatures under microwave irradiation are simulated in the resistively, capacitively, inductively shunted junction (RCLSJ) model including white noise. The simulated results as function of microwave power clearly show the appearance of Shapiro steps. It is shown that higher steps are suppressed for low microwave amplitudes. The rounding of the Shapiro steps observed experimentally has been reproduced by taking noise into consideration in RCLSJ model.     

Sulfur Hydrides: Phase Diagram and the Transition into the Record-High <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Bold">c</Emphasis></Subscript> State

Remarkable feature of the phase diagram of sulfur hydrides, the record-high T _c superconductors, is a sharp increase near P ≈ 150 GPa from T _c ≈ 120 to ≈ 200 K. This increase is a signature of the structural transition. The present study is concerned with the nature of this phase transition. One can demonstrate that the symmetry analysis along with an analysis of the impact of lattice deformations lead to the conclusion that we are dealing with the first-order transition. Such a transition is manifested in an abrupt appearance of small pockets on the Fermi surface and, correspondingly, the two-gap energy spectrum.     

Effect of an Elliptical Inclusion on Critical Current Density of a Long Cylindrical High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductor

An analytical investigation is presented to display the distribution of critical current flow and trapped magnetic field around an elliptical nonsuperconducting inclusion within a long cylindrical superconductor. The current streamlines, the critical current density, and the trapped field around the inclusion in the superconductor without deformation are obtained based on the Bean model and the method of conformal mapping. The results show that the critical current density of a superconductor will be decreased dramatically due to a macroscopic nonsuperconducting inclusion. Besides, the maximum trapped magnetic field is limited by the inclusion.     

Investigation of Reflectance Properties in 1D Ternary Annular Photonic Crystal Containing Semiconductor and High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Bold">c</Emphasis></Subscript> Superconductor

In this paper, we present the theoretical investigation and study of reflectance properties in a 1D ternary annular photonic crystal (TAPC) containing a semiconductor and a high-temperature superconductor. The proposed structure consists of alternate layers of indium nitride (InN), Bi₂Sr₂CaCu₃O₈ (BSCCO), and air placed in free space. A reflectance spectrum of the TAPC is obtained by employing the transfer matrix method (TMM) in the cylindrical waves for both transverse electric (TE) and transverse magnetic (TM) polarized waves. From the study of reflectance spectra, it is observed that the reflection band of the annular photonic crystal depends on the azimuthal mode number m in addition to other parameters. It is found that for azimuthal mode number m = 0, the width of the reflection band of the annular photonic crystal is the same as that of a planar photonic crystal (PPC). When the azimuthal mode number increases, the width of the reflection band increases at higher m values (m >5) for TE waves. In the case of the TM wave, it is interesting to observe that a superpolariton gap is created for a higher value of the azimuthal number (m >0). Further, we see the effect of the starting radius (ρ ₀) on the reflection band of the TAPC structure at the given m number for both TE- and TM-polarized waves. Finally, the effect of temperature on the reflectance spectra for both TE and TM waves at the given ρ ₀ and azimuthal mode has been studied.     

Skyrmion mechanism of hole pairing in the high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> cuprates

A topological mechanism of hole localization as two skyrmions in the CuO₂ layers of high-T _c superconductors is suggested on the basis of a nonlinear σ model.     

An Exponential Model for Critical Current Density Through a Low-Angle Grain Boundary in a High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Bold">c</Emphasis></Subscript> Superconductor

An analytical investigation is presented to display the distribution of critical current flow through a low-angle grain boundary in a high-T _c superconductor such as YBCO or Bi-2212 film. When a superconductor is subjected to a transport current or a magnetic field, the fluxoids are redistributed between the dislocations which comprise a low-angle grain boundary. A model considering the elastic interaction between a flux line and an edge dislocation is developed in this paper. Results of our model are consistent with those of the classic exponential model, while for high-angle grain boundaries with the misorientation angles ?? > 4^°, this model is invalid. It is helpful by using our model to understand the mechanisms of the effect of low-angle grain boundaries on critical current density.     

The Boundary Effect on the Energy Gap of High <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

Spatial dependence of the pairing potential across the thickness of the superconducting CuO₂ planes in high T _c superconductors (HTSC) copper oxides is found by using the Ginzburg-Landau-Gor’kov (GLG) theory. The potential turned out to be significantly suppressed due to an effect of non-superconducting layers, which separate the CuO₂ planes. The effect leads also to the reduction of the critical temperature of these superconductors. The temperature dependence of the effective energy gap was calculated in this work.     

The Temperature Evolution of the Inhomogeneous Magnetic Response of Cuprate Superconductors Above <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>

Many different experiments and probes have displayed some form of anomalous behavior that may be related to charge inhomogeneity in different families of cuprate superconductors. In some materials, it appears to be associated with charge density waves and in others as local static domains of varying densities. The doping and temperature evolution of such charge instability is a matter of current intense research. We present here a model based on a phase separation transition to the temperature evolution of transverse field muon spin relaxation (TF- μSR) magnetic inhomogeneous response of cuprates above T _c recently measured.     

Evolution of Phononic Band Gaps in One-Dimensional Phononic Crystals that Incorporate High-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> Superconductor and Magnetostrictive Materials

In this work, we calculate the reflectance of one-dimensional phononic crystals (1D PnCs) using the transfer matrix method. We present numerical results for two different PnC structures, the first one, PnCs1, contains high- T _c superconducting compound (Bi-2223) and the second, PnCs2, contains a giant magnetostrictive material (Terfenol-D). Magnetostriction is a property of ferromagnetic materials that causes them to change their shape/dimensions when subjected to external magnetic field. PnC studies that dealt with such materials are few. In this study, we focus on discussing the effects of the temperature and the magnetic field on the phononic gaps of these PnCs. For PnCs1, numerical results show that local resonant modes of elastic waves with brilliant sharpness can be realized. In addition, increasing the temperature leads to a decrease in the gap width which can be controlled by the magnetic field due to the effect of the magnetic field on the velocity of waves in the high- T _c superconducting compound, the magnetic field effectively can widen the gap. For PnCs2, numerical results show that the gap width increases by increasing the magnetic field because the magnetostrictive material directly expanded in the presence of the magnetic field.     

Specific Heat Jump at T<Emphasis Type="Italic">c</Emphasis> of High T<Emphasis Type="Italic">c</Emphasis> Superconductors: Effect of Van Hove Singularity

In the BCS framework, exact expressions for the ratio between the jump in the specific heat at T _c and the normal phase specific heat are derived within the Van Hove singularity scenario. Analytical results are obtained for an isotropic s-wave and anisotropic d-wave pairing symmetries. Graphical solutions of the ratio as functions of ω _D /T _c and E _F /T _c , where ω _D is the cutoff energy and E _F is the Fermi energy, show significant deviations from the BCS value of 1.43.     

Stress Intensity Factor <Emphasis Type="Italic">K</Emphasis><Subscript>I</Subscript> and <Emphasis Type="Italic">T</Emphasis>-Stress Determination in HDPE Material

For the characterization of high-density polyethylene (HDPE) pipes according to the operating conditions, the Nol ring test is an adequate method to rapidly and inexpensively determine the mechanical properties with good effectiveness. In this work, Nol ring tests will be carried out on HDPE material with different crack depth ratios. Based on these results, the brittle fracture of HDPE will be studied and a new experimental technique for measuring stress intensity factor (SIF) and T-stress under mode I conditions is developed. The formulation of the normal strains, close to the crack tip, is given using the first five terms of the generalized Westergaard formulation. Then, in a second step, these formulations are applied to analytically determine the optimum locations for the rectangular rosette to eliminate the errors due to higher order terms of the asymptotic expansion.     

Methods of Extracting Current Density Dependence of the Effective Activation Energy <Emphasis Type="Italic">U</Emphasis><Subscript>eff</Subscript>(J) in High <Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> Superconductors

We have reviewed the methods of extracting current density dependence of the effective activation energy U_eff(J) from experimental data, including transport measurements and magnetic relaxations. Then we applied the method proposed by Maley etc. on our single-phase HgBaCaCuO-1223 sample to obtain the effective activation energy. The effective activation energy U_eff(J, H = 1~T) is extracted from the magnetization relaxation data. On the other hand, U_eff(J) can be theoretically estimated for the model of a sinusoidal washboard potential in superconductors. By comparing the two results we believe that the single curve obtained in the former way can be seen as real current density dependence of effective activation energy U_eff(J). In addition, we have analyzed the reasons why the magnetic decay data at various temperatures can be scaled onto a single curve. The pinning mechanism in the measured temperature range does not change, and the activation energy depends separately on the three variables: T, B, and J are thought as two important factors for this. In the temperature close to zero and near T_c, thermally assisted flux motion would no longer valid since other processes predominate.     

Half-Metallicity and High-<Emphasis Type=Italic>T</Emphasis><Subscript>c</Subscript> Ferromagnetism in Si-containing Half-Heusler Alloys

A possibility of half-metallic ferromagnetism for the homogeneous phase in the half-Heusler alloy-based DMS CoTi_1−x Fe _x Sb is predicted. A phase diagram of the spinodal and binodal decomposition is constructed through the evaluation of the mixing free energies. By applying the Monte Carlo simulation method to the Ising model with realistic chemical pair interactions between Fe magnetic impurities, we simulate the spinodal decomposition and nanoscale separation in this alloy.     

Correlation Between <Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> and Hyperfine Parameters of Fe in Layered Chalcogenide Superconductors

Although pairing mechanism in unconventional superconductors is still an open question, the density of states at the Fermi level is considered to be one of the factors affecting the superconducting transition temperature. Herein, we report on ⁵⁷Fe-Mössbauer studies of β-FeSe, FeSe _0.5Te _0.5, and Rb _0.8Fe _1.6Se ₂ superconductors as well as two intercalate products consisting of FeSe layers and a lithium-containing molecular spacer in between. In these materials, the hyperfine parameters of ⁵⁷Fe are directly related to the 3d-electron density on Fe atoms and show strong correlation with superconducting properties.     

Performance enhancement in high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> ceramics through melting by Joule heating,infrared lamps,and laser radiation

We have analyzed experimental data on the effect of short-term melting followed by recrystallization on the microstructure and critical current density of YBa₂Cu₃O_{7 ? x} , Bi₂Sr₂CaCu₂O_{8 ? x} , and Bi₂Sr₂Ca₂Cu₃O_{10 ? x} high-T _c ceramics. The ceramics were melted using different heat sources: infrared lamps, laser radiation, and electric current. A significant increase in the critical current density of Bi₂Sr₂Ca₂Cu₃O_{10 ? x} ceramics (by a factor of 40 at 20 K and by a factor of 8 at 77 K) was achieved using cw CO₂ laser irradiation. Melting TiC-doped (0.1%) Bi₂Sr₂Ca₂Cu₃O_{10 ? x} ceramics with a CO₂ laser, followed by annealing, insured an even larger increase in critical current density: by a factor of 35 at 77 K. We have calculated the thickness of the molten layer produced by laser heating of high-T _c ceramics.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.