4M-2000A高温超导电缆制冷系统

介绍了我国新研制成的首条双通道热绝缘型 4 M- 2 0 0 0 A高温超导电缆制冷系统。该系统由 G- M制冷机提供制冷量 ,过冷液氮为冷却介质 ,通过液氮泵循环 ,组成一个闭式循环制冷系统。给出了制冷系统的调试结果。系统上装有温度、压力、流量、液位等测量仪表 ,并备有一个减压抽空系统 ,以附加提供制冷量     

Ultrasonic studies of aluminium-substituted Bi(Pb)-2223 superconductors

The compositional dependence of elastic properties of Al³⁺-substituted Bi(Pb)-2223 superconducting system with the general formula Bi_1.7−x Al_xPb_0.3Sr₂Ca₂Cu₃ O_y (x = 0.0, 0.1, 0.2 and 0.3) have been studied by means of ultrasonic pulse transmission (UPT) technique at 1 MHz (300 K). The elastic moduli of the specimens are computed and corrected to zero porosity. The observed variation of elastic constants with aluminium substitution has been explained on the basis of the strength of interatomic bonding. The applicability of heterogeneous metal mixture rule for estimating elastic constants and transition temperature has been tested.     

Coating of superconducting.123 compound on silver substrate by electrophoretic technique

Superconducting 123 powders have been deposited on silver metal wire and foil by an electrophoretic deposition technique, followed by appropriate heat treatment, to obtain superconducting wires and tapes. At the present stage the critical current density is rather low (85 A/cm²), however there remains a considerable scope for improvement.     

高温超导YBCO带材的交流损耗的FEM仿真分析

对高温超导带材YBCO的交流损耗进行了仿真分析。运用有限元FEM方法,基于Maxwell方程组的数值建模,引入了基于实验数据的power-law对交流损耗进行计算。首先对自场下的交流损耗值进行了仿真计算并分析了带材的电流密度与磁场分布情况,并通过与实验测量数据做比较验证仿真方法的有效性。其次分别对不同幅值下的平行场与垂直场下的交流损耗进行了计算,将自场、平行场以及垂直场下的电流密度与磁场强度的分布以及交流损耗值进行了对比分析。     

Electronic states near fermi level in superconductors La2 − x Sr x CuO4 by means of x-ray absorption spectra near Cu-K and La-L edges

The electronic states of La_{2? x} Sr _x CuO₄ with 0.00 ≤ x ≤ 0.20 are studied by means of X-ray absorption spectroscopy (XANES, EXAFS) near the K-edge of Cu²⁺ ion and the L-edges of La³⁺ ion. It is found that characteristic white lines occurring near L _II and L _III edges of La³⁺ ion show a slight energy shift depending on substituted Sr²⁺ ions, x and temperature. The white lines suggest that unoccupied high-density 5dπ and 5dδ bands of La³⁺ ion just above a Fermi level transform to a hybridized single band of 5dπδ at 78?K in the superconductors with x = 0.10, 0.16 and 0.20. On the other hand, the XANES spectra near the Cu-K edge including a pre-edge region do not depend on x and temperature in the region of 0.00 ≤ x ≤ 0.20. It is considered that there is no reconstruction of electronic states at the Fermi level in a Mott–Hubbard band gap between an O 2p valence band and a Cu 3d conduction band. The electronic states at the Fermi level are probably consisted of the unoccupied 5dπδ band and an empty charge-transfer 3d?⁹ L band at low temperature, bands of which occur in a band gap between a filled O 2p valence band and an unoccupied O 2p conduction band. The insulator–superconductor–metal transitions in La_{2? x} Sr _x CuO₄ are related to the 5dπδ and 3d?⁹ L bands and holes, which site at a top region of the O 2p valence band near the Fermi level produced by a substitution of La³⁺ with Sr²⁺ ions.     

A theorem for the existence of Majorana fermion modes in spin-orbit-coupled semiconductors

We prove an index theorem for the existence of Majorana zero modes in a semiconducting thin film with a sizable spin-orbit coupling when it is adjacent to an s-wave superconductor. The theorem, which is analogous to the Jackiw-Rebbi index theorem for the zero modes in mass domain walls in one-dimensional Dirac theory, applies to vortices with odd flux-quantum in a semiconducting film in which s-wave superconductivity and a Zeeman splitting are induced by proximity effect. The momentum space construction of the zero-mode solution presented here is complementary to the approximate real space solution of the Bogoliubov-de Gennes equations at a vortex core (Sau et al., arXiv:0907.2239 [17]), proving the existence of non-degenerate zero-energy Majorana excitations and the resultant non-Abelian topological order in the semiconductor heterostructure. With increasing magnitude of the proximity-induced pairing potential, the non-Abelian superconducting state makes a topological quantum phase transition to an ordinary s-wave superconducting state which no topological order.     

Superconducting properties in Rh17S15 under magnetic field and pressure

We have studied superconducting properties by measuring the electrical resistivity and magnetization for a single crystal of Rh₁₇S₁₅ with a superconducting transition temperature T_c=5.4 K. The upper critical field H_c2(0) and the lower critical field H_c1(0) were obtained as 20.5 and 0.0033 T, respectively. Correspondingly, the coherence length and the penetration depth were estimated to be 40 and 4900 Å, respectively, indicating that Rh₁₇S₁₅ is a typical type-II superconductor with strong correlations of conduction electrons with a 4d-electron character of Rh atoms. The present electron correlations are formed to be enhanced with increasing pressure.     

Random resistivity network calculations for cuprate superconductors with an electronic phase separation transition

The resistivity as a function of temperature for high temperature superconductors is very unusual and, despite its importance, lacks a unified theoretical explanation. It is linear with the temperature for overdoped compounds but it falls more quickly as the doping level decreases. The resistivity of underdoped cuprates increases like that of an insulator below a characteristic temperature where it shows a minimum. We show that this overall behavior can be explained by calculations using an electronic phase segregation into two main component phases with low and high electronic densities. The total resistance is calculated from the various contributions through several processes of random picking of the local resistivities and using a common statistical random resistor network approach.     

A novel method of flat YBCO rings development for shield-type superconducting fault current limiters fabrication

The application of flat superconductor rings has been investigated in the structure of inductive shield-type high temperature superconducting fault current limiters, HT_c-SFCL. A laboratory scale inductive shield-type HT_c-SFCL has been designed and fabricated using flat superconductor rings. The fabrication process has been fully presented. YBCO powder has been used for the fabrication of superconductor rings. This fabrication process, being quite innovative, is introduced completely. The method of the trapped field measurement has been used for the critical current density measurement of the fabricated superconductor rings. The device with nominal current of 2 A was tested in a 30 V circuit. The SFCL successfully limited the fault currents of up to 10 times the nominal current to an approximately fixed value of 3 A. The voltage-current characteristic of the fabricated prototype has also been obtained and has shown compatibility with the fault current limitation results.     

双Tl-O层Tl-Ba-Ca-Cu氧化物超导体的能带结构

利用EHT近似下的紧束缚能带结构计算方法计算了Tl-Ba-Ca-Cu氧化物超导体双Tl-O层体系的能带结构。计算结果表明费米面在a~*b~*面上是封闭的, 费米能级上电子态密度的增加和体系转变湿度(T_c)的提高是相一致的。Cu-O面上Cu和O的净电荷有规律的变化说明, Cu-O面上Cu和O的离子价态可影响该体系的超导电性。