Surface resistance and far infrared absorptivity at T=7 K of highTc YBaCuO superconductors

A surface resistance as small as R_S=3×10^–2 Ohms has been computed at T=8 K, for v=0.6 Thz (v=20 cm^–1), for an YBaCuO film deposited on an MgO substrate. The calculations are made with the refractive index computed from the Far IR transmission spectra of a 400 Å thick film.Still lower values are obtained with another sample, 300 Å thick of exceptional quality (R_S=1.2×10^–2 Ohms).     

Numerical and theoretical evaluations of AC losses for single and infinite numbers of superconductor strips with direct and alternating transport currents in external AC magnetic field

AC losses in a superconductor strip are numerically evaluated by means of a finite element method formulated with a current vector potential. The expressions of AC losses in an infinite slab that corresponds to a simple model of infinitely stacked strips are also derived theoretically. It is assumed that the voltage-current characteristics of the superconductors are represented by Bean’s critical state model. The typical operation pattern of a Superconducting Magnetic Energy Storage (SMES) coil with direct and alternating transport currents in an external AC magnetic field is taken into account as the electromagnetic environment for both the single strip and the infinite slab. By using the obtained results of AC losses, the influences of the transport currents on the total losses are discussed quantitatively.     

Phase diagram of the La–Si binary system under high pressure and the structures of superconducting LaSi5 and LaSi10

The La–Si binary phase diagram under a high pressure of 13.5 GPa was experimentally constructed. New superconducting silicides LaSi₅ and LaSi₁₀ were found, which have peritectic decomposition temperatures at 1000 and 750 °C, respectively. The single crystal X-ray structural analysis revealed that there are two polymorphs in LaSi₅. The α-form obtained by heating a molar mixture of LaSi₂ and 3 Si at about 700 °C or by a rapid cooling from 1000 °C under pressure crystallizes with the space group C2/m and the lattice parameters a=15.11(3), b=4.032(6), c=8.26(1) Å, and β=109.11(1)°. The β-form obtained by a slow cooling from 800–950 °C to 600 °C under pressure has the same space group but with slightly different lattice parameters, a=14.922(7), b=3.906(2), c=8.807(4) Å, and β=107.19(1)°. The β-form is formed during the incomplete transformation of the α-form on cooling, and has always been obtained as a mixture with the α-form. The compound can be characterized as a Zintl phase with a polyanionic framework with large tunnels running along the b axis hosting lanthanum ions. In the β-form, three of the five Si sites are disordered. The two polymorphs contain one dimensional sila-polyacene ribbons, Si ladder polymer, running along the b axis. The α-form showed superconductivity with the transition temperature T_c of 11.5 K. LaSi₁₀ crystallizes with the space group 6₃/mmc and the lattice parameters a=9.623(4), c=4.723(3) Å. It is composed of La containing Si₁₈ polyhedra (La@Si₁₈) of hexagonal beer-barrel shape, which form straight columns by stacking along the c-axis via face sharing. One-dimensional columns of La@Si₁₈ barrels are edge-shared, and bundled with infinite Si trigonal bipyramid chains via corner sharing. The Si atoms in the straight chains have a five-fold coordination. LaSi₁₀ became a superconductor with T_c=6.7 K. The ab initio calculation of the electric band structures showed that α-LaSi₅ and LaSi₁₀ are metallic, and the conduction electrons mainly come from Si-3p orbitals.     

d+s波超导体磁掺杂转变

研究了Anderson掺杂极限Δs/Δd《1的情况下,d+s波对称下的超导态。此模型包括哈密顿量中类似BSC项和自恰平均场似下的Anderson掺杂。随着掺杂中心数的增加或比率Δs/Δd的减小,可推出从低能下在费米能级附近具有双峰的态到N(0)≈(Δs/Δd)2态的转变。如果掺杂共振的能量为最小能量标度,则转变不连续。     

一种多通道超导测试系统的设计与实现

为了实现对超导带材和超导电力装置的电压、电流、温度等信号的快速精确测量,设计了一种超导测试系统的方案并进行了实验验证。该测试方案是根据超导电力实验特点,并基于系统开关、数字万用表和电源等现有仪器,在虚拟仪器环境下,实现了超导体多路测试量的实时采集与远程监控。实验结果表明,该测试系统可以快速准确探测电气信号,为超导体的交流损耗、稳定性裕度等测量提供可靠的前提条件。     

Al NMR studies of NpPd5Al2

We present ²⁷Al NMR studies for a single crystal of the Np-based superconductor NpPd₅Al₂. We have observed a five-line ²⁷Al NMR spectrum with a center line and four satellite lines separated by first-order nuclear quadrupole splittings. The Knight shift clearly drops below T_c. The temperature dependence of the ²⁷Al nuclear spin-lattice relaxation rate shows no coherence peak below T_c, indicating that NpPd₅Al₂ is an unconventional superconductor with an anisotropic gap. The analysis of the present NMR data provides evidence for strong-coupling d-wave superconductivity in NpPd₅Al₂.     

Mössbauer study of the (Ru1-xFex)Sr2GdCu2O8-δ system and two of its possible impurities: SrRuO3 and Gd2CuO4

Mössbauer spectra of a series of samples of the weak ferromagnetic $ {\left( {Ru_{{1 - x}} Fe_{x} } \right)}Sr_{2} GdCu_{2} O_{{8 - \delta }} M?ssbauer spectra of a series of samples of the weak ferromagnetic system reveal the existence of three dissimilar sites where the Fe atoms can go into the structure. The M?ssbauer parameters of the three observed quadrupole doublets, together with the relative population on each site, allow the following site assignment for the iron atoms: Fe³⁺ in four-fold planar coordination at Ru sites; Fe³⁺ in five-fold pyramidal coordination also at Ru sites and Fe²⁺ or Fe³⁺ in five-fold coordination at Cu sites. This assignment implies the formation of oxygen-vacancies at the charge reservoir (the RuO₂ planes) that affect the structure and the superconducting and magnetic properties of the undoped system. Moreover, a close correlation between the oxygen content, calculated through the M?ssbauer data, and the measured cell volume is established. We also report the M?ssbauer spectra of two compounds (SrRu_0.95Fe_0.05O₃ and Gd₂Cu_0.95Fe_0.05O₄) that could be formed as impurities during the synthesis of our samples.     

Manipulation of magnetic carriers for drug delivery using pulsed-current high Tc superconductors

An innovative method of manipulating magnetic carriers is proposed, and its feasibility for drug delivery and therapy is demonstrated experimentally. The proposed method employs pulsed-field solenoid coils with high-critical- temperature (T_c) superconductor inserts. Pulsed current is used to magnetize and de-magnetize the superconductor insert. The proposed method was demonstrated to be able to (1) move magnetic particles, ranging in size from a few millimeters to 10 μm, with strong enough forces over a substantial distance, (2) hold the particles at a designated position as long as needed, and (3) reverse the processes and retrieve the particles. We further demonstrated that magnetic particles can be manipulated in a stationary environment, in water flow, and in simulated blood (water/glycerol mixture) flow.     

100 GHz mixer vertically integrated (stacked) SIS junction array

A Vertically Integrated Array (stacked array) of single windowSIS junctions (VIA SIS), based on a stacked five layer structure of Nb-AlO_x-Nb-AlO_x-Nb, has been fabricated and tested in a quasi optical mixer configuration at 106 GHz. This particular VIA SIS design has two stacked junctions fabricated by standard tri-layer process employing photolithography, reactive ion and wet etching processes. A simple expression for calculating the specific capacitance of single and arrayed SIS junctions is suggested. Due to the absence of interconnection leads between the individual junctions and reduced overall capacitance, compared to a single SIS junction, has the VIA SIS good future prospects for use in submillimeter wave SIS mixers The VIA SIS may be regarded as a lumped rather than a distributed structure at least up to the gap frequency at 730 GHz for Nb. DC-IV measurements show high quality of the Individual SIS junctions and good reproducibility of the array parameters over the substrate area. The first VIA SIS mixer experiments yielded a receiver noise temperature of 95 K (DSB) at a LO frequency of 106 GHz.     

Liquid phase epitaxy of REBa2Cu3O7−δ single-crystalline thick films

The growth of REBa₂Cu₃O_7−δ (REBCO = rare earth elements) high-temperature superconducting thick films by liquid phase epitaxy is reviewed, which are most promising for electronic device and coated conductor applications. The paper focused on thermodynamic relations, chemical reactions and physical phenomena in the liquid phase epitaxy process, which are closely related to the control of the microstructures and properties of materials. Recent progresses achieved and the problems to be solved have been reviewed in above sections.