Tc负离子质谱分析技术及应用

由于Tc7．3V的高电离电位，采用传统的正离子质谱测量方式极为困难。世界上，仅Los Alamos实验室开展过Tc的负离子质谱分析技术研究。本年度采用新型发射剂，建立了Tc的负离子质谱分析技术。并利用该技术结合同位素稀释质谱法标定了人工生产的^97Tc稀释剂。     

高温超导体霍尔效应和温度关系的动态测量

本文采用了改进的动态测量方法，对高温超导体的霍尔效应与温度的关系进行了测量。该方法有效地降低了测量误差，并且简单快速。我们利用低廉、普及的普通电磁铁代替了液氦制冷的低温超导磁体，测量了高温超导体YBa2Cu3O7(YBCO)薄膜和Hg1-xBa2CaCu2O6 δ（Hg-1212)薄膜的霍尔效应。发现了在Hg-1212中，随汞的含量不同，超导临界温度Tc变化很大，但是霍尔角却几乎不变。相反，随氧的含量不同，霍尔角变化很大，而超导临界温度Tc却变化很小。Tc的变化被认为与CuO2面上的单胞空穴密度Psheet相关联。这对了解高温超导的机制很有意义。     

过渡金属元素X（X=Mo，Tc，Ru）掺杂单层GaS的第一性原理研究

近年来，二维GaS由于其优异的性质引起了科研人员的关注.基于密度泛函理论计算了过渡金属元素X(X=Mo, Tc, Ru)掺杂单层二维GaS的电子结构、磁性性质及光学性质.计算结果表明：单层GaS材料为间接带隙的非磁性半导体，在对S位点进行替位式掺杂后，Ga-rich和S-rich条件的形成能均为正数，导致过渡金属元素Mo、Tc和Ru不能自发地进入进入单层GaS材料中.所有掺杂体系都引入了杂质能级，杂质能级主要由掺杂原子的4d轨道贡献.掺杂后所有体系的带隙都有所减小，上自旋和下自旋的能带结构不再对称，使得Mo掺杂体系呈现半金属铁磁性，Tc和Ru掺杂体系呈磁性半导体特性，Mo、Tc和Ru掺杂后的总磁矩分别为4μ_B, 3μ_B和2μ_B,磁矩主要由掺杂原子的局域磁矩产生.掺杂后单层GaS的静介电常数得到提高，吸收谱出现红移，在可见光区和近红外区的吸收系数变大，对可见光的利用率增强.     

直接耦合双耦合环高温超导dcSQUID中增大有效面积的图形设计

设计和制作了一种新型的双耦合环的直接耦合高Tc dc SQUID结构。根据Y.Zhang等在高Tc rf SQUID中用图形填充内孔使电感减小的原理，在直接耦合dc SQUID中，用在耦合环内孔中图形填充的方法减小电感，进而增大Ap/Lp，以增大总的有效面积。用双晶衬底所做的对比实验表明，对于我们所设计的几何结构，有效面积增大了17%。     

高T_cNb-Ge超导膜的制备及分析

用直流吸气溅射法获得了Tc1)起始等于23K的Nb-Ge膜.对样品进行了分析,初步总结了高Tc-A15Nb3Ge的成相规律,对与Tc密切相关的因素进行了讨论. 引 言 很多A15型化合物具有超导电性且其超导转变温度Tc很高.1973年,Gavaler首次用直流低电压,高Ar气压力溅射法获得Tc起始温度为 22K的     

Mo(d,x)~(95m)Tc,Mo(d,x)~(96g),Tc和Mo(d,x)~(97)Tc反应的激发函数

用活化法和迭靶技术,测量了入射氘核能量从3.2到13.3MeV范围内,Mo(d,x)~(95m)Tc,Mo(d,x)~(96g)Tc和Mo(d,x)~(97m)Tc反应的激发函数,并与复合核统计模型理论计算作了比较。     

Bi2Sr2CaCu2O8+δ单晶超导临界温度的各向异性

研究了具有不同氧含量的Bi2Sr2CaCu2O8 δ单晶超导临界温度的各向异性,通过测量沿ab面和c轴的电阻率发现,在轻欠掺杂到过掺杂区域,单晶沿ab面和c轴的Tc值是比较接近的,但在重欠掺杂区,沿ab面的Tc值比c轴的Tc明显高,从平衡态的相位涨落模型可以得到,由于涨落效应对 c轴的临界电流密度的压制作用比对ab面的要强,导致了Tc的各向异性,但这种模型无法解释重欠掺杂超导体中ab面和c轴的Tc如此大的差别,我们认为重欠掺杂超导体中的相位涨落行为不同于其他掺杂超导体中的行为,实验和理论上都值得进一步深入研究。     

探索高Tc超导新材料的可能途径

本文从已有的实验与理论研究成果出发,分析和讨论了主导铜氧化物超导体转变温度Tc及其微观机制的各种外在和内禀的因素,在此基础上提出了进一步探索高Tc超导新材料的几种可能途径.     

周期脉冲序列调制色噪声作用下单模激光的光强关联时间

采用周期矩形脉冲信号直接调制色噪声作用下的单模激光增益模型,运用线性近似的方法计算得到了模型输出光强的自关联函数和关联时间(Tc),并讨论了光强关联时间随噪声强度和调制脉冲信号的变化关系.研究结果发现:噪声关联程度λ＜0时,光强关联时间Tc随噪声强度Q、D及脉冲信号的振幅A的变化曲线均出现了随机共振现象,系统的涨落达到最小,而在λ≥0时,Tc单调变化;在-1＜λ＜1范围内,Tc随噪声关联时间τ和信号的脉冲宽度θ的变化曲线也均出现了随机共振现象,且随λ的减小,共振现象越明显;Tc随信号周期T的变化却出现了抑制现象,λ越小,抑制作用越强.     

高Tc超导材料R—T曲线的动态测量

引言 Y·Ba·Cu·O超导材料的出现,使超导体的转变温度Tc提高到90K以上,当前由于大学物理实验在超导体转变温度Tc测试方面还是个薄弱环节,我们设计了动态测量高Tc超导体转变温度的实验装置,测量Y·     

SiC掺杂MgB_2的烧结过程及其动力学分析

SiC掺杂MgB2体系由于其优异的超导性能而受到普遍关注并成为超导领域中一大研究热点,但是目前的研究大多集中在SiC对MgB2超导性能的影响上,对SiC的加入对MgB2烧结过程的影响研究很少.本文结合差热分析和物相鉴定,系统研究了SiC掺杂MgB2体系的烧结过程,并在此基础上探究了其反应动力学机理.结果表明,在烧结过程中Mg先和B发生反应,随着温度的升高在Mg和B还没有反应完全的时候SiC和Mg继而开始反应.反应动力学分析表明该体系的固相反应阶段为相界面控制反应过程,其表观活化能为547.5KJ/mol,指前因子为5.76×1015min-1.     

外场中超导结的直流约瑟夫逊电流的计算

外加磁场对超导体/半导体/超导体结的临界电流有一定影响。超导结的临界电流与磁场的曲线非常类似于单色光在单狭缝衍射的夫琅和费图样。该文在未考虑外加磁场的超导体/半导体/超导体结的临界电流的基础上,进一步对外加磁场的情形进行了研究,并对其结果借助M athem atica软件做了进一步的讨论。     

Observation of selective surface element substitution in FeTe_(0.5)Se_(0.5) superconductor thin film exposed to ambient air by synchrotron radiation spectroscopy

A systematic investigation of oxidation on a superconductive Fe Te_(0.5)Se_(0.5)thin film,which was grown on Nb-doped SrTiO_3(001) by pulsed laser deposition,has been carried out.The sample was exposed to ambient air for one month for oxidation.Macroscopically,the exposed specimen lost its superconductivity due to oxidation.The specimen was subjected to in situ synchrotron radiation photoelectron spectroscopy(PES) and x-ray absorption spectroscopy(XAS) measurements following cycles of annealing and argon ion etching treatments to unravel what happened in the electronic structure and composition after exposure to air.By the spectroscopic measurements,we found that the as-grown FeTe_(0.5)Se_(0.5)superconductive thin film experienced an element selective substitution reaction.The oxidation preferentially proceeds through pumping out the Te and forming Fe–O bonds by O substitution of Te.In addition,our results certify that in situ vacuum annealing and low-energy argon ion etching methods combined with spectroscopy are suitable for depth element and valence analysis of layered structure superconductor materials.     

YBCO在热冲击条件下的失超特性研究

在实际的超导电力装置运行过程中,超导带材可能由于电力系统中诸如系统短路故障等各种动态过程,承受短路大电流、不平衡电流的冲击,以及由此而产生的电磁、机械应力、热量的作用而失超,因此,研究热冲击对超导材料性能的影响对超导电力装置失超保护非常重要.本文以第二代高温超导(YBCO)带材为样品,模拟实际超导电力装置中带材的绝热环境,通过外加电源对超导带材进行热冲击,研究YBCO带材在不同情况的热冲击条件下的失超过程以及带材温度和超导性能的变化.试验结果表明:对于美国Superpower公司生产的YBCO工程带材,瞬时温度超导300K后,带材的临界电流下降,瞬时温度超过500K,带材可能出现烧断现象.     

To the theory of the superconductive phase in rare earth metal compounds

Using the theory of the superconductive phase in rare earth metal compounds, we have considered the thermodynamic, highfrequency and kinetic properties of the rare earth superconductors both in paramagnetic and in superconductive states. The superconductive phase transition temperature was calculated on the basis of the two-band model. It is shown that an increase in critical temperature is possible.     

Spin glasses on the basis of rare earth metal compounds

A new class of materials is constructed of rare earth metals and their compounds by introduction of a large number of defects into the crystal lattice-dislocations and unelastic disclinations. It is shown that superconductive phase state is possible in these materials having spin glass magnetic structure. A technique of such a state observation is suggested.     

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.     

Probing decoherence with electromagnetically induced transparency in superconductive quantum circuits

Superconductive quantum circuits comprise quantized energy levels that may be coupled via microwave electromagnetic fields. Described in this way, one may draw a close analogy to atoms with internal (electronic) levels coupled by laser light fields. In this Letter, we present a superconductive analog to electromagnetically induced transparency that utilizes superconductive quantum circuit designs of present day experimental consideration. We discuss how a superconductive analog to electromagnetically induced transparency can be used to establish macroscopic coherence in such systems and, thereby, be utilized as a sensitive probe of decoherence.     

利用BFEL研究高温超导钇钡铜氧薄膜的中远红外特性

 报导了一种钇钡铜氧（YBCO）高温超导薄膜中远红外光探测器。在中远红外波段，利用北京自由电子激光对其响应特性进行了实验研究。对于微桥尺寸为210μm×70μm×0.3μm的样品,测量了电压响应、谱响应和时间响应。实验表明，在液氮温度下工作的YBCO高温超导光探测器不仅具有快速响应、较高灵敏度的特点，而且具有良好的宽带特性和较好的稳定性。     

The similarities between thin sputtered films and high-Tc superconductive ceramics

The system which will be considered in this paper is the thin film having, in a specific way, a modulated mass distribution along a given direction as consequence of the sputtering treatment. The theoretical analysis demonstrates that this system has some particular properties, which are very similar to the properties of the high temperature superconductive ceramics. Therefore, taking into account their layered structure, we propose to consider the sputtered high temperature ceramic as a system of thin sputtered film-blocks. The blocks, depending on the film thickness as well as on the results of the sputtering treatment, could exhibit (SP-blocks) or not exhibit (N-blocks) superconductive properties. Here, the word “superconductive” has a particular meaning, because the superconductive state is in fact the normal state with no phonons, as well with no Cooper pairs. Namely, due to the freezing of the low energy acoustical modes which arises in the SP-blocks, the current in these blocks could be considered as a superconductive one because the carriers propagate in the media with no phonons.

The above mentioned model assumptions lead to results which give possible explanations for the following particular properties of high T_c ceramics: the great carrier effective mass, the small value of the Fermi level, the anisotropy of the superconductive properties, the strong pressure dependence of T_c, the increasing of T_c with the increasing of the number of layers in the elementary cell, the existence of the specific heat jump and the dependence of the superconductive properties on the stoichiometric proportions x and δ.