高温超导体中的交流损耗

考虑到陶瓷高温超导体的颗粒物性 ,详细研究了 Bean- london模型及 Anderson- kim模型在分析高温超导体交流损耗方面的缺陷 ,提出了一种新的计算方法。用这种方法预期的损耗规律与文献报道的实验结果一致。另外 ,分析了超导体尺寸、晶间临界电流、晶粒尺寸和晶内临界电流对高温超导体交流损耗的影响     

Two-Band Model for High Tc Superconductivity

A two-band model is dealt with by the canonical perturbation theory of projection operators. An effective Hamiltonian with Cu-Cu, Cu-O and O-O couplings is obtained. A unified treatment for such a coupled system gives the variations of transition temperatures for Cu-Cu, Cu-O and O-O parings with the concentration of O-holes. A window of δ for superconductivity is obtaihed and compared with experimental data qualitatively and quantitatively.     

高温超导体中的短程反铁磁自旋关联

传统超导体具有大的相干长度 ,借助于由隧穿测量给出的电流 -电压关系 ,可以反演出电声子相互作用的谱密度α2 Ｆ(ω) .对于高温超导体来说 ,情况完全不同 ,它的相干长度很短 ,为要研究其中的相互作用谱密度 ,最好的办法是采用红外光反射率测量或进行中子非弹性散射实验 .最近 ,美国橡树岭 (ＯａｋＲｉｄｇｅ)国家实验室的Ｐ .Ｃ .Ｄａｉ等 ,对ＹＢａ2 Ｃｕ3Ｏ6 ｘ(ＹＢＣＯ)系列样品 ,给出了中子非弹性散射研究的新数据 .结果表明 ,短程反铁磁自旋关联 ,在超导形成中起着重要的作用 .中子散射与Ｘ射线散射的区别主要在于 :Ｘ射线散射的强…     

On the Spin-Bag Theory of High Tc Superconductivity

The properties in the spin-bag mechanism of hige T_c superconductivity are studied in the SDW background. It is found that if the Coulomb repulsive potential is much smaller than the valence-band width and is not beyond a particular range determined by the bag energy, two doped holes can be pairing via sharing a common bag. The transition temperature has a maximum value of the order 200 K for reasonable parameters but is independent of doping concentration. In addition, the ratio of the energy gap to T_c is found to be the same as the BCS value. Finally, the specific heat jump at the transition temperature, the coherence length and the upper critical field are roughly estimated.     

Flux States,Anyons and High Tc Superconductivity

In this paper, we studied the statistical behavior of anyons with isospin degrees of freedom, in which the fluctuation of isospjn degrees of freedom satisfies the O(3) nonlinear σ model. Under the mean field treatment, this model is in somewhat equivalent to the doped or frustrated Heisenberg an tiferromagnetic (AFM) model. We also studied the relation between the statistical field A_μ, and Skyrmion current B_μ. Finally, we set up the relation between flux states and spinon statistics, and the conditions of Bose condensation of holons. In particular, for π-flux state of A_μ, the spinons are bosons, the holons satisfy 2/3 fractional statistics.     

Superconductivity Mechanism of Non-Cuprate Superconductors

Based on the mechanism of charge fluctuation, the effective Hamiltonian is, derived to discuss the superconductivity for the non-cuprate compound BaPb_1-xBi_xO₃. The desired T_c versus δ curve is obtained. It is shown that the explanation of superconductivity for non-cuprate superconductors is the same as that of cuprate ones. Furthermore, that the non-cuprate superconductors have no ferromagnetism and anti-ferromagnetism can be explained, and the superconductivity windaw is due to the Cooper pairirtg in coordinate space.     

高温高压合成顶角氧掺杂型高温超导系列

 简要介绍了(Sr,Ca)_n+1Cu_nO_2n(Cl,O)₂,即三元数法的Cl-“02n”（或四元数Cl-02(n-1)n）超导系列,简称Cl-系超导体。和通常的高温超导体不同,Cl-系的电荷库由卤化物构成,而非通常的氧化物。即Cl-系的导电区和电荷库由顶角氯连接,根据这一结构特点用“顶角氧”掺杂,高压合成了T_c≈80 K的(Sr,Ca)₃Cu₂O₄(Cl,O)₂超导体。该化合物具有和全氧化物高温超导体可比的超导性能,表明高温高压合成全新的卤氧超导新材料的潜力,以及开发卤氧化物高温超导体群的研究前景。     

区域熔炼法制备高 Jc Nd123超导体

】Nd1+ x Ba2 - x Cu3Oy超导体以其良好的 Jc- B特性倍受人们注目。文中用区域熔炼技术在空气下制备出取向良好的 Nd1+ x Ba2 - x Cu3Oy 块材 ,采用纯氩下高温退火的办法抑制固溶体的形成 ,得到了零电阻温度 94K、临界电流密度达 540 0 A/cm2 的超导体。讨论了进一步提高 Jc的可能途径是减少液相的流失并使 Nd4 Ba2 Cu2 O10 相均匀分布。     

On the Coexistence of Superconductivity and Magnetic Ordering in Unconventional Superconductors

It is demonstrated that the coexistence of superconductivity and magnetic ordering, occurring, for instance, in iron-based pnictides and uranium compounds, is not forbidden by classical Maxwell’s equations and London-type equations. It predicts simply that internal magnetization is allowed but localized magnetic moments are screened at distances of the order of the London penetration depth. A microscopic theory is considered for the case of ferromagnetic ordering, described in simple terms by electron-magnon coupling. For the sake of simplicity, we assume that itinerant electrons are not responsible for the magnetic ordering, but interact with phonon and magnon excitations, leading to an alternative Cooper pair channel. The temperature dependence and the isotope effect of the superconducting gap is also analysed.     

Screening-Dependent Study of Superconductivity in 3d-Transition Metals Binary Alloys Superconductors

In the present article, we report the screening-dependent study of the superconducting state parameters （SSPs）, viz. electron-phonon coupling strength A, Coulomb pseudopotential μ^＊, transition temperature TC, isotope effect exponent a, and effective interaction strength No V of 3d-band transition metals binary alloys superconductors have been made extensively in the present work using a model potential formalism and employing the pseudo-alloy-atom （PAA） model for the first time. Five local field correction functions proposed by Hartree （H）, Taylor （T）, Ichimaru-Utsumi （IU）, Farid et al. （F） and Sarkar et al. （S） are used in the present investigation to study the screening influence on the aforesaid properties. The present results of the SSPs obtained from H-screening are found in qualitative agreement with the available experimental data wherever exist.     

An Extended Model for Coexistence of Superconductivity and Paramagnetism in High-Tc Superconductors

In the present work, the total magnetization in superconducting state is separated into critical state and paramagnetic components in terms of an H（x）-dependent magnetic flux density. Utilizing this model, we reproduce successfully M-H curves measured by Sandu et al. [Phys. Rev. B 74 （2006） 184511] and Sandu et al. [J. Supercond. Incorp. Novel Magn. 17 （2004） 701] for different forms of Jc.     

高压下氢基超导体的研究进展

实现室温超导一直是人们长期追寻的梦想,寻找和合成出具有室温超导性的新材料已成为 凝聚态物理学家和材料物理学家的“圣杯”。近年来,随着理论和实验相继发现超导临界温度高于 200 K 的 H3S 和 LaH10,氢基超导体已逐渐成为实现室温超导的最佳候选,成为物理学、材料科 学等多学科研究的热点领域之一。在本文中,我们将概述超导材料的发展历史和几种典型超导材 料,重点介绍当前高压下氢基超导体的研究进展及面临的挑战,详细讨论中低压力范围氢基高温 超导体的设计思路,展望氢基超导体在低压甚至常压下实现高温乃至室温的可能性。     

高温超导体中的电-声子相互作用

1911年 ,卡末林·昂内斯在金属汞中发现了超导电性 .在之后的很长一段时间内 ,人们对其中的机理认识很少 .直到 195 7年 ,ＢＣＳ理论的发表才为超导电性奠定了理论基础 .传统理论认为 ,在转变温度Ｔｃ 以下 ,超导库珀对的密度随温度降低而不断增加 ,形成库珀对所需的电子 -电子吸引不是瞬时的和超距的 ,而是靠晶格振动的中介 (电子吸收或发射声子 ) .ＢＣＳ理论的实验验证实现于 2 0世纪 6 0年代 .俄罗斯物理学家Ｅｌｉａｓｈｂｅｒｇ以方程组的形式将电 -声子相互作用纳入ＢＣＳ理论 ,并对超导体的声子谱作出预言 .之后 ,ＭｃＭｉｌｌａｎ…     

Superconductivity and magnetism in dilute CdMn alloys. Strong depression in Tc

The superconducting transition temperature in dilute CdMn is depressed by 220K/at.% Mn. The Mn content was determined by Curie constant, resistance and atomic absorption measurements on the same sample. A small amount of the Mn is magnetically passive; the remaining Mn atoms have an effective magnetic moment of 4.80μ_B.     

硼在高压下的超导电性

20 0 1年 1月ＭｇＢ2 超导电性 (Ｔｃ～ 39Ｋ)的发现 ,重新燃起了人们研究轻元素超导电性的兴趣 .表 1给出了迄今已发现的轻主族元素超导体和它们的Ｔｃ.其中碳超导电性 (Ｔｃ ～ 5 2Ｋ)是通过场效应电荷转移技术对Ｃ60 晶体进行空穴掺杂而实现的 ;大块铍的Ｔｃ 原本仅 2 6ｍＫ ,但在亚稳态薄膜样品中 ,它增加到了 10 5Ｋ .硼在常压下是半导体 ,用 4 88ｎｍ的Ａｒ离子激光照射 ,它展现出强的光电导 ,具有 1 6ｅＶ的能隙 .最近 ,来自美国华盛顿Ｃａｒｎｅｇｉｅ研究所的Ｅｒｅｍｅｔｓ等发现 ,由 2 0面体团簇分子Ｂ12 键联而成的β型多晶…     

Critical Fields in High T c Superconductors

Using microwave methods one can determine upper critical fields which lie beyond the field of the laboratory magnet, and avoid ambiguities associated with the broadened transitions in high Tc superconductors.Antonijie Dulicic is Professor of Physics at the University of Zagreb and senior scientist at Ruder Boskovic Institute. He received his ph. D. in 1973 at the University of Zagreb. His postdoctoral research wa at edole polytechnique (paris), and later sabbatical visits included a Max planck Institute, Comell University, and the University of Stuttgart.Miroslaw Pozak is research associate at Ruder Boskovic Insititute, in Zagreb. He received his Ph. D. in 1992 at the University of Zagreb. As an alexander von Humboldt fellow, he carried out his postdoctoral research at the University of stuttgart.     

High spin states in91Tc

Zeitschrift für Physik A Hadrons and nuclei - A shell model calculation for the states of91Tc has been carried out using the (1g 9/2, 2p 1/2) model space with residual interactions determined...