Springer Science and Business Media LLC

We investigate how the interplay of quantum confinement and level broadening caused by disorder affects superconducting correlations in ultra-small metallic grains. We use the electron-phonon interaction-induced electron mass renormalization and the reduced static-path approximation of the BCS formalism to calculate the critical temperature as a function of the grain size. We show how the strong electron-impurity scattering additionally smears the peak structure in the electronic density of states of a metallic grain and imposes additional limits on the critical temperature under strong quantum confinement.

The phase component of Co2TiSb1−x Sn x is strongly dependent on the preparation method. The L21-type Co2TiSb1−x Sn x (x = 0.25, 0.5) alloys are successfully synthesized by the melt-spun method. And the microstructural properties of these ingots indicate that the Co2TiSb0.75Sn0.25 and Co2TiSb0.75Sn0.25 melt-spun samples exhibit the pure L21 phase. The thermal-elastic martensitic transformation has been experimentally observed in Co2TiSb0.75Sn0.25 alloy.

We have studied the normal and superconducting transport properties of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) ceramic samples. Four samples, from the same batch, were prepared by the solid-state reaction method and pressed uniaxially at different compacting pressures, ranging from 90 to 250 MPa before the last heat treatment. From the temperature dependence of the electrical resistivity, combined with current conduction models for cuprates, we were able to separate contributions arising from both the grain misalignment and microstructural defects. The behavior of the critical current density as a function of temperature at zero applied magnetic field, J c (T), was fitted to the relationship J c (T)∝(1−T/T c ) n , with n≈ 2 in all samples. We have also investigated the behavior of the product J c ρ sr , where ρ sr is the specific resistance of the grain-boundary. The results were interpreted by considering the relation between these parameters and the grain-boundary angle, θ, with increasing the uniaxial compacting pressure. We have found that the above type of mechanical deformation improves the alignment of the grains. Consequently the samples exhibit an enhance in the intergranular properties, resulting in a decrease of the specific resistance of the grain-boundary and an increase in the critical current density.

A new family of dynamic states are found in a stack of inductively coupled intrinsic Josephson junctions in the absence of an external magnetic field. In this state, (2m l +1)π phase kinks with integers m l ’s stack along the c axis and lock neighboring junctions together. A significant part of the dc power is pumped into plasma oscillations via kinks at the cavity resonances. The plasma oscillation is uniform along the c axis with the frequency satisfying the ac Josephson relation. Thus this state supports strong terahertz radiation and seems to be compatible with the recent experimental observations.

In this paper we analyze transport data of different families of Fe-based superconductors, within a pseudogap framework. The Fe(Te, Se) samples exhibit s-shaped resistivity ρ(T) curves, while SmFeAs(O, F) ones present a departure from their high-temperature linear behavior. In either case, a characteristic temperature can be identified. These temperatures correspond to those at which abrupt changes in the temperature behavior of Hall resistance and of Seebeck coefficient occur, suggesting that they are signatures of pseudogaps opening in the density of states. The direct correlation between these characteristic temperatures and the superconducting transition temperatures suggests that the pseudogap and the superconducting state originate from the same mechanism. Scaling procedures of resistivity curves confirm such proportionality. On the other hand, excess Fe content in Fe(Te, Se) samples affects the pseudogap temperature much more strongly than the superconducting T c . Finally, we find out that the pseudogap in the 1111 family is almost insensitive to disorder, as in high-T c cuprates.

In this work, Cu1−x Co x thin films with different x values are prepared by the electrodeposition technique. The deposition is carried out in a three-electrode cell using a potentiostat/galvanostat controlled by a computer potentiostatically. Cyclic voltammetry of electrolytes is performed in order to study electroplating process of the films. The films are deposited on Cu substrates in sulfate bath. The effects of different parameters such as bath composition, working electrode’s voltage, addition of sodium saccharin to electrolyte on composition, crystal structure and surface morphology of the films are investigated. The X-ray diffraction patterns reveal that all films have single phase face-centered cubic structures with no extra reflections due to the presence of pure Co or Cu clusters. Addition of sodium saccharin affects morphology of the films by changing the grain size, grain distribution, and grain shape. Magnetic analysis indicates that the saturation magnetization increases as the cobalt percentage increases, while coercivity decreases.

The mixed Li-ferrites with dopants Mn2+ and Cd2+ are synthesized by chemical co-precipitation method. Structural and morphology analysis with X-ray diffraction (XRD) and SEM, respectively, confirmed the spinel structure with uniform distribution of the nanoparticles of the size in the range 17–36 nm. The dopant concentration affects the lattice parameter by incorporating Cd2+, lattice parameter increases in the range 8.3–8.7 Å. This increase is attributed due to difference in ionic radii of cations. The dc electrical resistivity (ρ dc) and drift mobility (μ d) confirmed a semiconducting-like behavior. The increase in dopant concentration decreases the activation energy (ΔE). A small amount of Cd2+ causes a sudden increase in saturation magnetization (M s) and remanence (M r) values. It is observed that up to x=0.30 M s increases, while further incorporation of Cd2+ decreases magnetization. This is due to canted spin and can be explained on the basis of the canted spin model. The decrease in Curie temperature with increase in Cd2+ is due to interaction between tetrahedral (A) and octahedral (B) lattice sites.

The hoop stress/strain distribution is one of the key issues for construction of a high field, low temperature, and multicomponent superconducting solenoid magnet. Usually, the multicomponent solenoids belong to a multilayer composite structure, thus the change of hoop thermal strain during cooling is complex. On the other hand, the theory formula is widely used for the electromagnetic stress calculation of the coil, due to its simplicity. However, the assumption of this calculation makes it impossible to consider the effects of multifield, on stress of the coil. So, all kinds of stress/strain need be well explained by fine strain measurements. In this work, the mechanics characteristics of two multilayer coils in the multicomponent magnet, which were wound using NbTi/Cu and stainless steel wires, by hoop strain tests have been explored during cooling and excitation. According to the measurements of hoop strain, the structural mechanics of multicomponent superconducting solenoids were evaluated during the above two physical processes. The uniform of prestressing tension exerted during wounding can also be estimated by the recoverability of the solenoids using hoop stress measurements. The validness of the experimental methods was also confirmed by comparison with analysis results, which were obtained considering coupled and multilayer effect for the multicomponent superconducting coils. Moreover, the test method and numerical procedures for the hoop strain were also described and discussed.

We report on measurements of the tunneling conductance structures above the superconducting gap energy using YBa2Cu3O7 polycrystalline junctions. The measured second derivative data are reproducible among the junctions, and the intensities of the common structures at the biases of 37–38, 47–53, 67–77, and 94–95 mV are strong enough to be assigned. These structures are in agreement with those in the neutron phonon density of states in whole energy regions when the energies are measured from the gap edge of 26±1 meV. This correspondence indicates that the electron-phonon interaction contributes to the pairing mechanism of this superconductor.