各向异性超导体的Ginzburg-Landau理论

本文内容主要有二个方面 :1 )由各向同性均匀系的BCS理论扩展到各向异性非均匀系 ,并给出各向异性非均匀系的完整的GL方程式 ,定出了各个宏微观参量间的关系式。2 )结合层状结构氧化物超导体的导电层与非导电层相间的特征等 ,用有效调制势模型和电子有效质量近似 ,将各向同性均匀系的BCS理论较具体地扩展到各向异性非均匀系并进行深化研究。扩展理论所给出的临界温度和能隙方程公式 ,主要的热力学性质和电磁性质公式等应用到YBaCuO超导体上 ,理论结果与实验结果均相符 ,并也给出各向异性非均匀系的完整的GL方程式 ,与上面 1所给出的形式相同 ,也定出了各个宏微观参量间的关系 ,应用到YBaCuO超导体的一些主要性质上也与实验结果相符。     

各向异性超导体的Ginzburg-Landau理论

本文内容主要有二个方面：1）由各各同性均匀系的BCS理论扩展到各向异性非均匀系，并给出各种异性非均匀系的完整的GL方程式，定出了各个宏微观参量间的关系式。2）结合层状结构氧化物超导体的导电层在导电层相间的特征等，用有效调制势模型和电子有效质量近似，交各向同性均匀系的BCS理论较具体的扩展到各向异性非均匀系并进行深化研究，扩展理论所给出的临界温度和能隙方程公式，主要的热力学性质和电磁性质公式等应用到YBaCuO超导体上，理论结果与实验结果均相符，并也给出各向异性非均匀系的完整的GL方程式，与上面1所给出的形式相同，也定出了各个宏微观参量间的关系，应用到YBaCuO超导体的一些主要性质上也与实验结果相符。     

MgB2超导体的各向异性

采用两带Ginzburg-Landau(GL)理论模型,考虑到两能带有效质量的各向异性,我们讨论了各向异性超导体MgB:的上临界磁场各向异性比以及有效相干长度对角度、温度的依赖关系.     

掺杂对二硼化镁超导体上临界磁场的影响

采用二带Ginzburg-Landau(GL)理论模型,考虑到能带有效质量的各向异性,讨论了MgB2超导体的上临界磁场对角度、温度和相干长度的依赖关系.结果表明,替代杂质越多,上临界磁场越强,这与实验结果符合.     

MgB_2超导参量的研究

采用二带Ginzburg-Landau(GL)理论模型,考虑到能带有效质量的各向异性,讨论了MgB2超导体的相干长度ξ(T)、速率υc(T)、伦敦穿透深度λ(T)和临界电流密度j(T)对温度T和角度θ的依赖关系.     

基于PC机的虚拟现实技术研究

本文利用所需额外硬件很少的立体显示技术,研制了一种基于微机平台的虚拟现实系统。这个系统利用最新推出的微机版的三维图形标准Open GL建模,以实时动画形式实现了真正的交互性,立体视觉效果明显,可以给观赏者提供真实的临场感和亲自控制的参与感。与已研制出的“三维立体显示系统”相比,有了实质性的进步。     

用两带Ginzburg-Landau理论分析两带超导体Lu2Fe3Si5的表面临界磁场

用两带Ginzburg-Landau(GL)理论分析了Lu₂Fe₃Si₅的表面临界磁场,当超导体的表面与任一主晶面重合,且外磁场平行于超导体的表面时,比值H_c3/H_c2(H_C2是Lu₂Fe₃Si₅的上临界磁场)强烈依赖于温度. 当超导体的表面是bc平面,且 关键词： 两带超导体 GL理论 2Fe₃Si₅')" href="#">Lu₂Fe₃Si₅ 表面临界磁场     

多层共轴空心超导圆柱体(NSC)系统的GL泛函和磁通量子化

本文将N层共轴空心超导圆柱体系统作为一个整体而建立了Ginzburg-Landau(GL)泛函。在薄壁近似或弱磁场情况下求解GL电流方程。引入与含超导序参量的穿透深度和等效面积有关的类电感系数,给出了NSC系统类磁通量子化的具体表示式,它由N个磁通量子数n_1,n_2,…,n_N来表征,并在N=1,2时分别过渡到与单层和双层空心超导圆柱体(SSC和DSC)系统的类磁通量子化情形相一致的结果。     

天线理论中的第二类积分方程

本文提出一个决定柱状天线电流分布的新的积分方程,这是一个一维的Fredholm第二类积分方程。它不同于天线理论中惯用的Hallen积分方程。本文着重分析了在天线为无穷长时,由两个方程所解得的电流和磁场,说明第二类积分方程比Hallen方程更适于描述天线的实际情况。还初步进行了有限长度天线的数值计算,结果表明用第二类积分方程进行天线的数值计算是可行的。     

用两带Ginzburg-Landau理论分析超导材料Lu_2Fe_3Si_5的穿透深度

本文用两带各向异性GL模型计算了两带超导体Lu2Fe3Si5的穿透深度,当选取适当的参数时,在理论结果与实验结果符合的很好,并在此基础上计算了Lu2Fe3Si5在c方向的穿透深度与ab平面内的穿透深度的比值(γλ),结果表明γλ随温度的升高而降低,这点与MgB2不同.并且本文还讨论了在脏极限下γλ的情况.     

Surface induced mixed state of a superconducting film

Presented in this paper is a theoretical analysis of a planar surface induced mixed state for a superconducting film in parallel applied field. An analytical solution of the internal magnetic field is obtained based on Saint-James and de Gennes' order parameter in a film. An expression of Gibbs free energy per unit volume without restriction of a geometry is derived from non-linear Ginzburg-Landau (GL) equation in terms of a renormalized GL parameter and a modified geometric factor. Based on the Gibbs free energy, a phase diagram of distinguishing a first and second order phase transition for a type I superconducting film is calculated. The numerical results for exact solutions of spatial variation of order parameter, current density and internal magnetic field in the film geometry in parallel applied field case are presented. Near the upper critical field, the first entry of an applied field in the film exhibits a laminar structure.     

Remarks on Small Superconducting Specimens in Magnetic Field and Measurements of the Lower Critical Field

We shall discuss the magnetic behaviors associated with the boundary effects for type-Ⅱ superconductors in general orientations. Using previous results, we speculate that the relation among the lower critical field H_c1, the thermodynamic critical field H_c and the upper critical field H_c2, namely H_c²～H_c1H_c2, is still approximately valid for general experimental orientations. More precisely, the magnitudes of H_c1, H_c and H_c2 are consistent with the formulae given for bulk superconductors when the typical size of the superconducting specimen is greater than the coherence length ε, provided the penetration depth λ is substituted by a modified value λ_m. Consequently, the criterion for observing type-Ⅱ superconducting magnetic behaviors also becomes λ_m>ε, although the London equation is still governed by λ. In the second part of the paper, we shall also suggest an experiment, based on the fact of H_c1. of superconducting thin films in parallel magnetic field being much higher than that of bulk superconductors, to measure H_c1 precisely, especially for extreme type-Ⅱ superconductors,without influence of the penetration barrier.     

Some Features of Critical Parameters Calculations of Nonhomogeneous Superconducting Films Using the Ginzburg–Landau Theory

Bulletin of the Lebedev Physics Institute - A method for calculating the critical state of inhomogeneous superconducting films using the Ginzburg–Landau (GL) theory is proposed. From the...     

Aharanov-Bohm currents in thin superconducting cylinders

The Aharanov-Bohm effect is the influence of classically inaccessible electromagnetic fields on quantum wave functions. In this paper we consider the Ginsburg-Landau (GL) equations for the stationary states of a thin, superconducting cylinder in the presence of a curl-free, static electromagnetic potential corresponding to zero fields. We solve the GL equations explicitly to obtain self-consistent solutions for the current density, the induced field and the free energy in a well-defined and accessible approximation. The analysis makes quantitative predictions which can, in principle, be experimentally tested to provide a clear and convincing demonstration of the Aharanov-Bohm effect.     

三维介观超导环涡旋态的研究

通过数值求解非线性金兹堡-朗道(G-L)方程组,研究了三维介观超导环中的涡旋态。发现了在细环中只能存在巨涡旋态,以及存在顺磁、抗磁迈斯纳效应和间隙性超导现象。在粗环中,发现了多涡旋态和巨涡旋态共存的混合态。相应讨论有助于理解介观超导环中涡旋态相变。     

Editorial

Many excellent articles and textbooks on superconductivity have been published. However, concise and easily-handled data books written for scientists and engineers who work in the field of superconducting materials are very few. This article aims to collect and outline basic properties of superconducting materials and to provide such people with a database. The properties listed include crystal and electronic structures, equilibrium phase diagram, superconducting critical temperature, critical magnetic fields, critical current density, pinning force, specific heat coefficient, Debye temperature, penetration depth, coherence length, GL parameter, energy gap, electronic density of states at the Fermi level, electron-phonon coupling constant, Coulomb pseudopotential, and others. Emphasis is on the materials used in superconductive applications. Structural phase transitions such as martensitic transformations and transitions to the charge-density-wave state in superconducting materials are also reviewed. The properties of superconducting oxides will be summarized in the next article of this series.     

Logic of Quench Protection Assembly for BEPC-ⅡInteraction Region Superconducting Magnet

Two superconducting magnet complexes are used in BEPCⅡ interaction region. The corresponding quench protection system divides all related faults into two classes and takes different protection actions according to the urgency degree. Since BEPCⅡ has two operating modes and the superconducting magnets use different power supplies in different operating modes, the quench protection system must take the mode switching into consideration.     

The design simulation of the superconducting section in the ADS injector Ⅱ

The high-current superconducting proton linac is being studied for the accelerator-driven system (ADS) project undertaken by the Chinese Academy of Sciences. The injector Ⅱ will be operated at 162.5 MHz, and the proton out from the RFQ with an energy of 2.5 MeV will be accelerated to 10 MeV by two cryo-modules, which are composed of eight superconducting half wave resonance cavities and nine solenoids. In this paper, the design and beam simulation of the superconducting section of the injector Ⅱ, the acceptance calculation and a stability analysis are presented.     

Pulses in a complex Ginzburg-Landau system: Persistence under coupling with slow diffusion

The Ginzburg-Landau (GL) equation is essential for understanding the dynamics of patterns in a wide variety of physical contexts. It governs the evolutions of small amplitude instabilities near criticality. If the instabilities are, however, driven by two coupled instability mechanisms, of which one corresponds with a neutrally stable mode, their evolution is described by a GL equation coupled to a diffusion equation.In this paper, we study the influence of an additional diffusion equation on the existence of pulse solutions in the complex GL equation. In light of recently developed insights into the effect of slow diffusion on the stability of pulses, we consider the case of slow diffusion, i.e., in which the additional diffusion equation acts on a long spatial scale.In previous work [A. Doelman, G. Hek, N. Valkhoff, Stabilization by slow diffusion in a real Ginzburg-Landau system, J. Nonlinear Sci. 14 (2004) 237-278; A. Doelman, G. Hek, N.J.M. Valkhoff, Algebraically decaying pulses in a Ginzburg-Landau system with a neutrally stable mode, Nonlinearity 20 (2007) 357-389], we restricted ourselves to a model with both real coefficients and, more importantly, a real amplitude A rather than the complex-valued A that is needed to completely describe the pattern formation near criticality. In this simpler setting, we proved that pulse solutions of the GL equation can both persist and be stabilized under coupling with a slow diffusion equation. In the current work, we no longer make these restrictions, so that the problem is higher-dimensional and intrinsically harder. By a combination of a geometrical approach and explicit perturbation analysis, we consider the persistence of the solitary pulse solution of the GL equation under coupling with the additional diffusion equation. In the two limiting situations of the nearly real GL equation and the near nonlinear Schrödinger equation, we show that the pulse solutions can indeed persist under this coupling.