Status of Superconductivity

Superconductivity is potentially one of the most important scientific developments of this decade because it permits the attainment of very high magnetic fields with almost negligible cost in electrical power dissipation.The history, recent fundamental research, and developments in materials and devices which utilize this phenomenon are discussed. In addition, the implications of recent developments for various areas of technology and their applications are discussed.     

论薄膜的超导电性(英文)

应用Cheng-Born能带对称破缺理论和TFDC(Thomas-Fermi-Dirac-Cheng)电子理论研究了薄膜层内电子的特性.对金属铂上的TiO2膜层来说,TFDC理论指出电子(或空穴)将由金属与膜的间界面一侧迁移到另一侧.根据Cheng-Born对称破缺理论,当能带中只有很少的电子时,则只有极少的角区中存在电子,动量空间即产生对称破缺,从而导致超导电性,并由热力学估算出薄膜超导体的转变温度.结果显示薄膜超导体的转变温度至少比块材超导体的转变温度高一个量级.作者还设计了一个研究薄膜超导电性的实验.     

Superconductivity in rare earth and actinide compounds

Rare earth and actinide compounds and the extraordinary superconducting and magnetic phenomena they exhibit are surveyed. The rare earth and actinide compounds described belong to three classes of novel superconducting materials: high temperature, high field superconductors (intermetallics and layered cuprates); superconductors containing localized magnetic moments; heavy fermion superconductors. Recent experiments on the resistive upper critical field of high T_c cuprate superconductors and the peak effect in the critical current density of the f-electron superconductor CeRu₂ are discussed.     

Superconductivity and field induced states in DMET-TSeF family

The magnetoresistance and magnetization have been measured in (DMET-TSeF)₂X ( X = AuI₂, Au(Br)₂, AuCl₂, Au(CN)₂ and I₃) family. All of them have quasi one-dimensional Fermi surfaces at room temperature. It has been shown that two (AuI₂ and I₃) of them show superconductivity. We have also found three salts which show field induced spin density wave state, two at ambient pressure, and one under pressure. Another investigation is that I₃ salt is superconducting, but does not show FI-SDW nor Shubnikov-de Haas oscillation in spite of the comparatively large magnetoresistance.     

X-ray photoelectron spectroscopic study of π electron delocalization in polyphenyls — a comparison with acenes and polystyrene

High resolution core and valence X-ray photoelectron spectra of biphenyl, p-terphenyl, p-quaterphenyl and p-polyphenyl clarify the electronic structure of these aromatic compounds. Comparison with similar data for the lowest acenes (benzene, naphthalene, anthracene and tetracene) and polystyrene permits an evaluation of electron delocalization in relation to the electrical properties. Energy gaps of 5.8 eV for polystyrene and 4.0 eV for p-polyphenyl are obtained.     

铁磷族化合物及其超导电性

氟掺杂的LaFeAsO中26K超导电性的发现极大地促进了凝聚态物理的发展。在短短的两年时间中,已经有过千篇文章发表,已经有七种新结构被发现,超导转变温度也被迅速提升到了55～57K。此外,在超导机理方面这类化合物也已经被认定属于非常规,而反铁磁自旋涨落被认为是导致超导配对的媒介。从材料和物理学的角度对这类化合物的性质和超导机理给出了简单的综述。还对未来的研究及应用给出了一些展望。     

Superconductivity research and applications development at IGC

Intermagnetics General Corporation’s experience in producing high-quality metallic (NbTi and Nb₃Sn superconducting wires, tape, and cable provided the foundation on which it developed a process for manufacturing high-critical-transition-temperature superconductors. The product with the greatest near-term potential is silver-sheathed (Bi, Pb)₂Sr₂Ca₂Cu₃O_x, which is produced by the powder-in-tube process.     

Superconductivity of the quasi-one-dimensional semiconductor — polyacene

Superconductivity in polyacene with zero or small band gap is studied within the mean field approximation. It turns out that the BCS gap and the transition temperature are not exponential but proportional to the square of the interaction constant. Even if a band gap exists, superconductivity persists as long as the band gap is small. Interchain transfers reduce the BCS gap and the transition temperature.     

Superconductivity in quasi one-dimensional metals and the optimal phonon frequency

The transition temperature, T_s to singlet superconductivity in quasi one-dimensional metals is studied as a function of the phonon frequency ω₀. When both electron-phonon and electron-electron couplings are present, T_s has a maximum at a finite ω₀. When the electron-phonon interaction dominates and ω₀ is too small, superconductivity is eliminated by charge density waves, while if the electron-electron interaction dominates and ω₀ is too large, superconductivity is eliminated by spin density waves.     

Superconductivity and ferromagnetism in Pd doped Y9Co7

The ferromagnetic superconductor Y₉Co₇ was chemically doped to yield the solid solution Y₉Co_7-xPd_x for 0 < x < 0.4. The lattice parameter a does not depend on x, whereas c increases with increasing Pd content up to x = 0.2, the palladium solubility limit. The transition from ferromagnetism (T_C = 4.25 K) to superconductivity (T_sc = 2.4 K) was observed only for the parent Y₉Co₇ compound. For the lowest tested Pd doping level (x = 0.05), ferromagnetism is enhanced strongly (T_C = 9.35 K) and superconductivity is not seen above 1.8 K. The Curie temperature rapidly increases from 4.25 K to about 10 K for a Pd concentration of x = 0.1 and remains almost unchanged for Y₉Co_6.8Pd_0.2.     

不同金属位置掺杂的YBCO体系中两个结构块和超导电性的关联

根据块模型,对不同掺杂量的YBa2Cu3-xNixOy,Y1-xPrxBa2Cu3Oy和YBa2-xLaxCu3Oy体系内两个结构块的结合能进行了计算,研究了结合能和超导电性的关系。结果显示:3个体系中随掺杂量的变化,块间结合能和超导转变温度之间存在有趣的关联,即:随着掺杂量的增加,块间结合能增大,超导转变温度减小。同时在YBa2Cu3-xNixOy,Y1-xPrxBa2Cu3Oy和YBa2-xLaxCu3Oy体系中虽然有相似的结论,但也有源于不同元素在不同位置掺杂的差别。这不仅说明钙钛矿块和岩盐块间的相互作用在超导电性中起重要要作用,而且说明不同元素在不同位置的掺杂对超导电性有不同的影响。     

Superconductivity: A new window on plutonium’s complexity

Superconductivity has recently been discovered in a plutonium intermetallic compound (PuCoGa₅) at the surprisingly high temperature of 18.5 K. This article discusses the motivation that led to this discovery as well as what it implies for the understanding of both unconventional superconductivity and the metallurgy of plutonium. For more information, contact J.L. Sarrao, Los Alamos National Laboratory, MST-10: Condensed Matter & Thermal Physics, Mail Stop K764, Los Alamos, NM 87545; (505) 665-0481; fax (505) 665-7652; e-mail sarrao@lanl.gov.     

TiC掺杂12芯MgB2线材微观结构以及超导电性

采用 PIT工艺,以分步法粉末为装管前驱粉,选用中心铜铌复合棒增强的导体结构制备了TiC掺杂MgB2多芯线材,研究了不同热处理温度对于粉末相组成、线材的微观结构以及超导电性的影响,结果表明分步法粉末能够有效提高C原子的取代水平,同时芯丝中MgB2晶粒尺寸达到亚微米级,MgB2晶粒连结性较好,制备多芯线材在4.2 K,5 T时,其Jc仍高达3×104 A/cm2。     

价电子密度与Y123铜氧超导电性关系研究

通过X射线衍射、超导电性测试、氧含量变化、正电子湮没以及理论计算等方法,系统研究了金属离子掺杂的YBa2Cu3-x(Fe,Co,Al)xO7-δ(x=0.0~0.5)铜氧超导体的超导电性,为了比较也一并讨论了Zn掺杂样品的实验和理论结果。研究表明,超导转变温度Tc与样品中价电子密度无直接关联,与Hall实验揭示的Tc与空穴载流子浓度关系有同样结论,表明电声耦合机制在铜氧超导体中失效。因此,无论是空穴配对还是电子配对,仅仅是实现超导态的前提,并非其真正的决定因素。如果铜氧超导微观机制依然沿袭"电声耦合"理念很可能误入歧途。