压力对不同Tc的Bi2+xSr2Ca1-xCu2Oy单晶超导电性的影响

 在研究BiSrCaCuO超导单晶的过程中，我们发现材料的实际化学组分与理想的2212相配比组分有着一定的差别，正是这种成分偏析造成了样品的T_c与结构的不同。本文研究了在压力下不同T_c的样品随压力改变T_c的变化关系，发现偏析越大、T_c越低的样品的dT_c/dp也越大，而越接近理想组分，则dT_c/dp越趋于最小值，还可以从此推断出BiSrCaCuO理想单晶材料的T_c最佳值。压力对超导电性的这种影响可能与耦合链长的变化有关。     

一维多通道正常金属结构的透射几率

本文考虑一个严格一维的正常金属多分支结构,指出把Büttiker等人处理两分支结构的方法加以改进。即可解决这种多分支结构问题。我们给出了多分支结构的透射系数公式,作为一个简单的例子,求出了一个对称三分支结构的具体结果,并表明在这种结构中存在透射几率的共振现象。 关键词：     

探索高临界温度超导体

一、临界温度需要而且也是 可能提高的 超导体问世已经六十年了.对其机制的认识和使之变成有应用价值的新材料还只是近二十年的事.超导体虽然受到要求在极低温度下工作的限制,但由于它具有独特的性质,使它在某些方面的应用显示出无可匹敌的优越性,而受到人们重视.在电力工程上,若建立强场的磁体或者与强磁体大电流有关的设备(如电机),使用普通的良导体,不仅消耗巨大的能量,更重要的是由于发热而带来的冷却散热问题,这就限制了设备容量的提高.我国自行设计制造的双水内冷汽轮发电机组,正是解决了冷却问题,才提高发电容量的.超导体是唯一的直…     

重电子体系及其超导电性

在本刊第 15卷第 1期,章立源[1]对重费米子系统及其超导电性已经作了介绍.在该文的基础上,本文主要谈及有关的一些实验和不寻常的性质,也简述目前在解释这些实验现象时提出的一些理论,作为补充. 一、一些实验结果1.正常态的性质 让我们来看一看实验中观察到的重电子材料在低温下的一些与一般金属迥然不同的性质.先看电阻率ρ.在300K往下,通常金属的电阻率从 1到 10 μΩ·cm开始,随温度降低很快.而在重电子材料中,ρ在室温下约为10μΩ·cm,并随温度降低而上升,一般在50K以下会有一个极大值,然后才随T→OK下降. 图1给出 CeCu2Si2,UBe13;…     

高临界温度超导体的探索

本文将在[1],[2]的基础上进一步介绍探索高温超导体的有关问题.第一节介绍电子-声子机构的有关问题.第二节介绍界面超导性、非晶态材料超导性和颗粒超导性等一些目前感兴趣的问题.第三节介绍激予超导性.弟四节介绍其它新机构. 一、电子-声子机构超导性 关于超导电性的理论是基于如下认识:金属中处于费密面附近具有相反动量和自旋的两个电子,由于和晶格之间相互作用而互相吸引,形成电子对,结果在临界温度Tc之下金属呈超导电性.因为晶格振动是以量子化的声子形式存在的,因此这种机构叫电子-声子机构. 通常用　方程描述T.(见[1]的(5.1)(5.2)式…     

Nb-Ti-Zr固溶体系列的比热与超导电性

本文给出Nb-Ti-Zr三元固溶体的比热测量数据及其电荷转移模型分析。关于临界温度变化规律的讨论,模型与实验定性符合,定量上的某些差异可能来自于αTi-βTi的相变。     

IRREVERSIBILITY LINE AND THERMAL DEPINNING IN YBa2Cu3O7-δ

By measuring magnetic torque moment in a field-sweeping process, the temperature and field dependence of the critical current density j (with a criterion of electric field) and the normalized relaxation rate Q = d lnj/d ln E of a YBa₂Cu₃O_7-δ thin film were obtained. With a minimum current density (j_min = 10A·cm^-2) the irreversibility lines at different sweeping rates were determined. It was found that these irreversibility lines cannot be fitted to either the melting line or the vortex-glass transition. All the data can be interpreted by the thermally-assisted-flux-flow model. Further investigation shows that, at irreversible tem-perature and field, U_c is much smaller than k_BT, which indicates that the thermal depinning is the real origin of the irreversibility line.     

Ⅱ类超导体的平面钉扎模型

提出一件钉扎模型。将按此模型导出的钉扎力公式与实验结果进行了比较。     

Structural and physical properties of undoped and nickel-doped BaFe2-xNixAs2（x = 0,0.04） single crystals

<正>Single crystals of undoped and nickel-doped BaFe_(2-x)Ni_xAs_2(x=0,0.04) have been grown by FeAs self-flux method.The maximum dimension of the crystal is as large as ~ 1 cm along the ab plane.The crystalline topography of a cleaved crystal surface is examined by scanning electron microscope(SEM).By x-ray powder diffraction(XRD) experiments using pure silicon as an internal standard,precise unit cell parameters(tetragonal at room temperature) are determined:a = 3.9606(4) A(1 A=0.1 nm),c = 13.015(2) A for BaFe_(1.96)Ni_(0.04)As_2 and a = 3.9590(5) A,c = 13.024(1) A for BaFe_2As_2.DC magnetization and transport measurements are performed to check superconducting transition(T_c=15 K for x=0.04) and other subtle anomalies.For BaFe_(0.96)Ni_(0.04)As_2 crystal,the resistance curve at normal state shows two distinct anomalies associated with spin and structure transitions,and its magnetization data above ~ 91 K exhibit a linear temperature dependence due to spin density wave(SDW) instability.     

Floating-zone growth and property characterizations of high-quality La2-хSrхCuO4 superconductor crystals

We have grown underdoped(x=0.11,0.12) and optimally doped(x=0.16) La2 x SrxCuO4 single crystals by the traveling-solvent floating-zone technique.In order to prepare good quality cuprate crystals,we have made much effort to optimize the preparation procedures.For example,we haveadopted the sol-gel route to prepare a highly fine and homogeneous La2xSrxCuO4 precursor powder for fabricating a very dense ceramic feed rod used for the floating-zone growth,and we have also used quite a slow growth rate.The high quality of the grown crystals has been verified by double-crystal x-ray rocking curves,with the full-width-at-half-maximum being only 113-150 arcseconds,which are the best data reported so far for La2xSrxCuO4 crystals.The superconducting critical temperatures of the grown crystals are 30,31 and 38.5 K for x=0.11,0.12 and 0.16 samples,respectively,according to magnetic measurements.