Alternating-current losses in two-layer superconducting cables consisting of second-generation superconductors coated by U-shaped ferromagnetic materials

Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by either a non-magnetic or strong ferromagnetic material having a U profile is numerically investigated. Computations are carried out through the finite-element method. The alternating-current losses do not increase significantly if the relative permeability of the coating is increased three orders of magnitude, provided that the current amplitude is less than half of the critical current in a superconducting wire. However, the losses are much higher for ferromagnetic coating if the amplitude of the applied current oscillating at 50 Hz is close to the critical current. The ferromagnetic coating is seen to accumulate the magnetic field lines normally on its surfaces, while the field lines are parallel to the long axes of the wires, leading to more significant flux penetration in the coated regions. This facilitates a uniform low-loss current flow in the uncoated regions of the wires. In contrast, coating with a non-magnetic material gives rise to a considerably smaller current flow in the uncoated regions, whereas the low-loss flow is maintained in the coated regions. Moreover, the current flows in opposite directions in the coated and uncoated regions, where the direction in each region is converse for the two materials.     

The magnetism for NN AFM ground state in Fe-based superconductor: Sr1−xKxFe2As2

The crystal structure, magnetism properties, and density of states for FeAs layered compound SrFe₂As₂ have been investigated by using the density functional theory (DFT) method. The magnetism under a checkerboard nearest neighbor anti-ferromagnetic (NN AFM) and ferromagnetic (FM) order ground-state have been analyzed with substitution for Sr with K ion in Sr_1−xK_xFe₂As₂. The results indicate that the distortion of FeAs tetrahedrons is sensitive to the electron doping concentration. The system magnetism was suppressed by K doping in NN-AFM ground state instead of FM. The density of states at Fermi level N(E_F) under NN AFM ground state would be regarded as a driving force for the increased T_c of Sr_1−xK_xFe₂As₂ system as observed experimentally. Our calculation reflects that NN AFM type spin fluctuation may still exist in the Sr_1−xK_xFe₂As₂ system and it may be an origin of strong spin fluctuation in this system besides the spin density wave (SDW) states.     

超导滤波器制作与可靠性初步试验

介绍了高温超导滤波器薄膜电极与同轴转接器用金带连接技术,得到了较高的性能指标,所制作滤波器带内回波损耗<-21dB.并将金带连接效果的仿真指标与实测结果作了对比,指标一致性较好.所制超导滤波器顺利通过振动冲击试验,表明器件具备一定的可靠性.     

Design and performance of a compact superconducting duplexer at VHF-band

This paper presents the design, fabrication, and performance of a compact high temperature superconducting duplexer at VHF-band. The duplexer consists of a T-junction and two four-pole filters with an ultra-narrow bandwidth of 400 kHz at 216 MHz and 220 MHz, respectively. By using gap-coupled feedlines in the filter design procedure, the duplexer is constructed by connecting the two filters using a T-junction with short-length branches. The two filters are fabricated on separate substrates and are carefully packaged to achieve a high isolation between the duplexer channels. The duplexer has a compact size of 41.6 mm × 28 mm. The measured results at 73 K show a high performance. The return loss is −17 dB, the insertion losses of both channels are less than 0.16 dB, and the out-of-band rejections are higher than 60 dB. The isolation between the two channels is better than 76 dB.     

Doping and temperature dependence of electronic Raman response in cuprate superconductors

The doping and temperature dependence of the electronic Raman response in cuprate superconductors is studied within the kinetic energy driven superconducting mechanism. It is shown that the temperature dependent depletion at low-energy shifts is faster in the B1g symmetry than in the B2g symmetry. In analogy to the domelike shape of the doping dependent superconducting transition temperature, the maximal peak energy in the B2g channel occurs around the optimal doping, and then decreases in both underdoped and overdoped regimes. Moreover, the overall density of Cooper pairs increases with increasing doping in the underdoped regime.     

量子色动力学在有限温度密度区间的相结构(英文)

本文综述量子色动力学在有限温度密度区间的相结构,包括高密条件下的色超导态和在高温条件下相对论重离子碰撞实验中产生的强耦合夸克-胶子等离子体。我们简要地介绍在相对论重离子碰撞实验中发现强耦合夸克-胶子等离子体的历史,并且讨论用体粘滞系数与熵的比值确定QCD临界点的可能性。对于在高密区域的相结构,我们着重讨论错位配对情况下的非标准色超导态,解释无能隙色超导态的色磁不稳定性、Sarma不稳定性和Higgs不稳定性.     

Deforming and moving a vortex by the tip of a magnetic force microscope

Recent experiments [O.M. Auslaender et al., Nat. Phys. 5 (2009) 35] use a magnetic force microscope not only to image but also to move and deform an individual vortex line in a bulk YBCO type-II superconductor. The theory of this experiment is presented accounting for pinning and curving of the vortex and for the full three-dimensional anisotropy of pinning and of vortex line tension in this material.     

Calorimetric study of molecular superconductor κ-(BEDT-TTF)<Subscript>2</Subscript>Ag(CN)<Subscript>2</Subscript>H<Subscript>2</Subscript>O which contains water in the anion layers

Thermodynamic investigation of an organic superconductor κ-(BEDT-TTF)₂Ag(CN)₂H₂O in which the BEDT-TTF dimers are arranged in the κ-type structure in the donor layers is performed by the relaxation calorimetric technique at low temperatures and under magnetic fields. A thermal anomaly related to the superconductive phase transition was observed at 5 K. The existence of residual γ^* in the superconductive state is about 18% of the normal state γ value, which is larger than those of κ-(BEDT-TTF)₂Cu(NCS)₂, and κ-(BEDT-TTF)₂Cu[N(CN)₂]Br salt. The lattice heat capacity reflected on the β-term in the low-temperature heat capacity was found to be affected by the cooling rate. The disorder produced in the network structure constructed by hydrogen bond in the insulating layer is considered to give low-energy phonon excitations reflected in the heat capacity.     

基于超导的全张量重力梯度敏感头设计

基于超导的迈斯纳效应与超导量子干涉技术,结合柔性并联机构理论,设计一种基于超导的全张量重力梯度敏感头。敏感头采用6个完全相同的同时具有移动与转动自由度的敏感结构,对称的布置在正六面体外,对称面的两个敏感结构相对旋转90°成垂直状态。轴向间距使两个敏感结构直接测量重力梯度轴向分量,相互垂直使两个敏感结构既可以测量重力梯度交叉分量,也可以测量共模角加速度。利用超导线圈的电感变化响应质量块位移,进一步通过超导回路将其转变为磁场变化,并由超导量子干涉器进行检测。敏感结构采用8分支的柔性并联机构支承,构成空间对称的形式,可以实现对称的力学特性,保证各处的柔性铰链产生均匀变形,减少非对称的偏移,避免单一铰链的应力集中,具有沿轴移动刚度与绕轴转动刚度小、非设计的寄生误差方向刚度大的优势。在惯性系下的全张量重力梯度值可由坐标变换得到,可以预期得到1E的测量精度。