三维介观超导环的涡旋结构

在Ginzburg-Landan理论的框架下, 运用有限差分法研究了在圆环电流产生磁场下的介观超导圆环内的涡旋结构, 讨论了超导圆环尺寸和不同空间分布的磁场对涡旋形成的影响, 得到在一般超导圆环体内的基态多是巨涡旋态、而多涡旋态多以激发态形式存在的结论, 说明磁场一般从超导圆环的环孔穿过, 而很难穿过超导圆环体.     

金属小颗粒的超导电性北大核心CSCD

采用两带Richardson模型,用随机矩阵理论方法研究了具有高斯能级分布的金属小颗粒的超导电性,计算了系统的熵、比热跃变和超导临界磁场.结果表明,带间相互作用有利于系统的超导电性,带间相互作用越强,超导临界温度越高,超导临界尺寸越小.大的基态自旋S不利于系统的超导电性,基态自旋S越大,超导临界温度越低,超导临界尺寸越大.对于S≠0的自旋基态,随着颗粒尺寸的减小只存在超导衰减现象,而对于S=0的自旋基态,则先出现超导增强现象,随后出现超导衰减现象.理论结果与实验符合.     

金属小颗粒的超导电性

采用两带Richardson模型,用随机矩阵理论方法研究了具有高斯能级分布的金属小颗粒的超导电性,计算了系统的熵、比热跃变和超导临界磁场.结果表明,带间相互作用有利于系统的超导电性,带间相互作用越强,超导临界温度越高,超导临界尺寸越小.大的基态自旋S不利于系统的超导电性,基态自旋S越大,超导临界温度越低,超导临界尺寸越大.对于S≠0的自旋基态,随着颗粒尺寸的减小只存在超导衰减现象,而对于S=0的自旋基态,则先出现超导增强现象,随后出现超导衰减现象.理论结果与实验符合.     

关于磁单极子通过超导线圈的讨论

1 问题的提出 1931年英国物理学家狄拉克从理论上预言了磁单极子的存在.1982年,美国物理学家卡布莱设计了一个寻找磁单极子的实验.他设想,如果一个只有S极的磁单极子从左向右穿过如图1所示的超导线圈圆环abcd,那么超导线圈中将会出现什么现象呢?     

金属小颗粒超导电性研究北大核心CSCD

采用两带Richardson模型,用随机矩阵理论方法研究了具有高斯能级分布的金属小颗粒的超导电性.结果表明,带间相互作用有利于金属小颗粒的超导电性.对于每一个自旋S基态,都存在着对应的超导临界尺寸lc,当金属小颗粒的线度小于lc时,超导电性消失;S越大,lc越大;对于S≠0的自旋基态,只有超导衰减现象,对于S=0的自旋基态,随着颗粒尺寸的减小,先出现超导增强现象,随后出现超导衰减现象,理论结果与实验符合.     

金属小颗粒超导电性研究

采用两带Richardson模型,用随机矩阵理论方法研究了具有高斯能级分布的金属小颗粒的超导电性.结果表明,带间相互作用有利于金属小颗粒的超导电性.对于每一个自旋S基态,都存在着对应的超导临界尺寸lc,当金属小颗粒的线度小于lc时,超导电性消失;S越大,lc越大;对于S≠0的自旋基态,只有超导衰减现象,对于S=0的自旋基态,随着颗粒尺寸的减小,先出现超导增强现象,随后出现超导衰减现象,理论结果与实验符合.     

磁场作用下超导圆环的涡旋演化

利用Ginzburg-Landau理论模拟在外磁场作用下超导圆环的涡旋演化,讨论了外磁场、材料参数以及圆环内外径对涡旋进入超导圆环体以及涡旋达到稳定分布的影响.研究结果表明:外磁场越大,材料参数κ越大,圆环环身越宽,则超导圆环体内容纳的涡旋就越多.当磁场较小时,涡旋只由内边界进入超导体,当磁场足够大时,涡旋则先由外边界,然后再从内边界进入超导体.     

大功率高温超导滤波器的设计与功率测试

本文在双面YBCO高温超导薄膜上设计并制备了两节大功率超导滤波器,根据滤波器功率承载能力与最大电流密度之间的关系,减小电流密度和分散电流密度的分布是提高功率承载能力的关键.本文采用增加超导谐振器尺寸、优化几何结构及改进馈线耦合方式的方法,设计了两节2 GHz频段梭型谐振器结构的滤波器.设计及测量结果显示了馈线结构及谐振器几何尺寸优化程度对超导滤波器功率承载能力有不同程度的影响,说明了在大功率超导滤波器设计中应选用无结点间隙耦合式馈线以抑制电流密度的聚集.采用优化后的谐振器结构制备的梭型两节超导滤波器经测试功率承载能力为2 W.超导滤波器的尺寸为25×12 mm LaAlO3基片,中心频率2.022 GHz,相对带宽为2.4%.同时给出了超导滤波器功率测试的结构和方法.     

超导材料的混沌现象

讨论了一维稳态和发展型Ginzburg-Landau(缩写为G-L)超导方程组,从数学上论证了常稳态解的不稳定性及无穷维动力系统在行波解意义下的极限集之存在性.指出G-L超导方程组描述的超导材料具有作者意义下的无穷维动力系统的混沌现象,即超导材料在传导中可能出现奇特现象 关键词： 超导材料 G-L超导方程组 无穷维动力系统 混沌现象     

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。     

Superconducting state evolution with applied magnetic flux in mesoscopic rings

The magnetic flux dependence of the vortex state for small mesoscopic superconducting rings surrounded by a medium is investigated by the phenomenological Ginzburg-Landau theory. The influences of the ring size and the surface superconductivity on the free energy and total supercurrent are studied. For narrow rings, the persistent current evolves towards a periodic behaviour with magnetic flux. The complete paramagnetic or diamagnetic state, corresponding to positive or negative current flowing in the whole ring, can occur. A remarkable intermittent superconducting behaviour for the ground-state transition is found when the strength of surface-suppressed superconductivity is enlarged or the ring size is decreased. Consequently, a pure superconducting state with positive total current can be obtained.     

In situ electrical transport measurement of superconductive ultrathin films

The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer Fe Se films has recently initiated a great deal of research interests in surface-enhanced superconductivity and superconductive ultrathin films fabricated on crystal surfaces. On account of the instability of ultra-thin films in air, it is desirable to perform electrical transport measurement in ultra-high vaccum(UHV). Here we review the experimental techniques of in situ electrical transport measurement and their applications on superconductive ultrathin films.     

On wetting transition in superconductivity

The existence of two solutions for proximity-induced superconductivity described by the Ginzburg-Landau theory is established in the general case. A first-order phase transition can occur between these states, resulting in superconductive wetting.     

On the possibility of superconductive transition in a strong magnetic field

The possible existence of triplet superconductive transition in metals in a strong magnetic field is shown. In such system in the sufficiently strong magnetic field there are no currents, which can destroy the superconductivity.     

Superconductivity in disordered thin films: giant mesoscopic fluctuations

We discuss the intrinsic inhomogeneities of superconductive properties of uniformly disordered thin films with a large dimensionless conductance g. It is shown that mesoscopic fluctuations, which usually contain a small factor 1/g, are crucially enhanced near the critical conductance g(cF) > 1 where superconductivity is destroyed at T = 0 due to Coulomb suppression of the Cooper attraction. This leads to strong spatial fluctuations of the local transition temperature and thus to the percolative nature of the thermal superconductive transition.     

Coexistence of superconductivity and magnetic order

Experimental work on systems showing evidence of the coexistence of superconductivity and magnetic order is reviewed. The presently known systems are shown to be “superconducting spin glasses” rather than “ferromagnetic superconductors”. In those systems where the magnetic order is expected to be long-ranged (up to now) superconductivity vanishes as soon as the magnetic order appears. But it is not excluded that magnetic order with a correlation length larger than the superconductive coherence length can coexist with superconductivity.     

Effect of pressure on superconductive properties of BaPb1-xBixO3 monocrystals

Abstract

Extraordinary properties of superconductive BaPb, -xBixO, (BPB) led to the assumption of out-of-ordinary mechanism of the superconductivity of localized pairs^1,2     

电磁感应理论在磁悬浮列车中的应用

介绍了电磁感应和超导基本理论的实际应用－磁悬浮列车。以日本超导磁悬浮列车为例，阐述其作用原理，介绍了超导磁悬列车的发展状况。指出在物理教学中，理论学习与实际应用相结合是提高学生学习兴趣和培养创新能力的有效途径。     

Ti-Pd系超导电性的研究

本文给出了Ti-Pd系超导转变温度随合金成份的变化规律,指出Ti-Pd系中超导性是Pd在α-Ti中的固溶体所贡献的,结合这个合金系的相图,讨论了这些结果,认为Pd在α-Ti中的极限固溶度应有较高的数值。 关键词：     

价层轨道平均能与掺杂铁基砷化物超导电性

文中研究了目前已掺杂的铁基砷化物的原子价层轨道平均能与超导电性的关系,发现全部阳离子和阴离子的价层轨道平均能的平均值主要集中在11.407 eV—11.705 eV之间,而阳离子与阴离子价层轨道平均能的平均值之差的绝对值主要集中在8.446 eV—8.869 eV之间,并由平均作用能与转变温度的关系推测出目前掺杂铁基砷化物还没有达到超导最佳状态。这将有助于了解晶格上电子的静电作用与超导机理的关系,并对以后铁基砷化物的掺杂研究有一定的指导意义。