基于高温超导双晶结的约瑟夫森效应观测实验

基于YBa2Cu3O7-δ高温超导双晶结,组建了约瑟夫森效应测试装置.利用此装置观察了直流和交流约瑟夫森效应,并测量了约瑟夫森结的临界电流和夏皮罗台阶.     

从金属原子气样本上观察到约瑟夫森效应

1962年由B·D·约瑟夫森首先在理论上预言了电子能通过两块超导体之间薄绝缘层的量子隧道效应，这个预言在一年之后得到了实验上的证实．为表彰约瑟夫森的理论预言，1973年授予他诺贝尔物理学奖，由此普遍称为约瑟夫森效应．该效应的内容得到充实和完善，应用也快速发展，逐渐形成一门新兴学科——超导电子学．两块超导体夹一层厚度适当的薄绝缘材料的组合称S-I-S超导隧道结或约瑟夫森结．约瑟夫森效应分为两种：     

约瑟夫森效应的发现

基于史料、阐述了约瑟夫森效应的发现过程。     

量子质量标准

评述了由于约瑟夫森效应及量子霍尔效应在计量工作中的应用,使质量计量工作进入"量子质量标准"新阶段.     

高温超导约瑟夫森效应演示仪

<正>设备组成:测量仪+样品+测量杆;测量仪:高温超导约瑟夫森效应演示仪微波源:固态微波发生器;频段:10GHz;最大输出功率:80mW;衰减器:最大衰减20dB;样品:高温超导晶界约瑟夫森结尺寸:10mm×10mm×1mm;工作温度:77K(液氮沸点温度)测量杆:采用快速真空接头的漏热式恒温器;工作温度:300K至77K;性能指标:能测量、显示高温超导约瑟夫森结和超导体的临界转变温度Tc和交直流约瑟夫森效应(约瑟夫森结的Ⅰ-Ⅴ曲线)。配置一些其它部件还可显示约瑟夫森电流随磁场的     

非传统超导体间的约瑟夫森隧道效应

本将用于液氦和Ｓ波超的准离子自洽场方法推广到非传统超导体，处理了有关的边界问题，并研究了非传统超导体间的约瑟夫森隧道效应，给出隧道结临界电流随两侧晶体相对取向改变而变化的定量关系。     

＂磁约瑟夫森效应＂的首次观察

两块超导体,中间用极薄的氧化层（绝缘层）隔开,便构成了所谓的“超导隧道结”．按照量子物理,超导库珀对应该有机会穿透氧化层的壁垒．这样,绝缘层看起来也是超导的——虽然有电流流过,但在绝缘层的两端却测不到电压．1962年,年仅22岁的英国剑桥大学研究生约瑟夫森（B．D．Josephson）,通过认真的理论推演,预言了上述隧道效应的存在．在以后的数年中,这个预言连同一系列相关的预言（统称为约瑟夫森效应）,作为量子力学在宏观世界同样适用的例证,均在实验中被证实,约瑟夫森因此获得了1973年度诺贝尔物理奖．     

相位与约瑟夫森效应及其在超导中的应用

 许多物理效应(如多普勒效应,约瑟夫森效应、ＡＢ效应、干涉效应、量子霍尔效应)都与相位紧密相关,且相位的物理效应已在很多领域中得到了验证和应用。本文就相位与约瑟夫森效应及其在超导现象中的应用进行分析和讨论。一、约瑟夫森效应当两块超导体之间所夹绝缘层的厚度很薄(10-7ｃｍ左右)时,两超导体中的电子对会因隧道效应而耦合,电子对将从一块超导体进入另一超导体,形成超导(隧导)电流,而两超导区的电子对波函数具有确定的相位关系,这种现象称为约瑟夫森效应。1962年约瑟夫森研究了两块超导体被一层薄绝缘层分开的Ｓ-Ｉ-Ｓ结,即超导的隧道结,从理论上预言将会有以下的物理效应。     

高温超导约瑟夫森结阵列的相位锁定

根据交流约瑟夫森效应,研究了嵌入Fabry-Perot谐振腔里的约瑟夫森结阵列在微波辐照下的相位锁定问题。结阵列是由生长在双晶钇稳定氧化锆(YSZ)基片上的YB2Cu3O7(YBCO)超导薄膜光刻成微桥得到的。通过优化设计,在温度为79.2K辐照频率为77.465GHz的条件下,包含620个串联约瑟夫森双晶结的结阵列在外加微波辐照下实现了相位锁定,得到了陡峭的夏皮罗台阶。其第一级夏皮罗台阶的电压约为0.1V,台阶高度约为0.17mA。试验结果表明,这种结阵列结构在电压基准的应用上有极大的优势,而且这种准光学耦合方法在太赫兹信号发生和检测方面有很好的应用前景。     

本征约瑟夫森结阵列的PSpice模型及混沌行为研究

建立了电容耦合本征约瑟夫森结阵列在电路仿真软件PSpice中的模型，利用这个模型对恒定电流驱动下的本征约瑟夫森结阵列进行了仿真研究.通过与不存在电容耦合的本征约瑟夫森结的时域波形、频谱、分维和相图等结果的对比，发现了本征约瑟夫森结阵列中的混沌行为.这一发现对于本征约瑟夫森结的理论和应用研究有重要的意义.     

Superconducting transport in an LED with Nb electrodes

Superconducting transport is measured between two superconducting electrodes at the n-type semiconductor side of a superconductor-based LED where a Josephson junction is formed. The characteristics of the Josephson junction are found to be modulated by applying voltage to the normal electrode at the p-type semiconductor side. The Josephson junction characteristics show an extraordinary sensitivity to the radiative recombination process, which we estimate as the recombination efficiency.     

Observation of inter-grain Josephson effects in Y-Ba-Cu-O samples

Josephson effects have been observed in bulk samples of Y-Ba-Cu-O. The magnitude of the zero-voltage current is found to change systematically with externally applied small magnetic fields of a few mG. It is also found to vary when samples are irradiated with microwaves. These observations suggest the presence of inter-grain Josephson junctions.     

An experimental study of Josephson effect in bulk YBaCUO

We have observed Josephson effect in bulk YBaCuO. The size of bulk is 7.5×2.2×0.3 mm and the microwave frequency is 9.82 GHz in our experiment. Several microwave induced steps can easily be observed. When an external magnetic field is applied to the bulk, the critical supercurrent at zero voltage is suppressed significantly. It has been demonstrated that YBaCuO bulk can be seen as a network of Josephson junctions. An experimental study of Josephson effect in bulk YBaCuO at millimeter wave frquency is in progress.     

Comments about the escape temperature representation of experiments on macroscopic quantum tunnelling

Summary The technique of analysing the data on macroscopic quantum tunnelling effects in Josephson junctions in terms of the escape temperature is discussed in connection with some important experiments. In particular we analyse the effect of an uncertainty on the determination of the Josephson critical current in the current dependence of the escape temperature. As a result we point out that the experimental errors are of the same order of the effect to be observed.     

超导体/正常金属/半导体/正常金属/超导体结的研究

在约瑟夫逊效应的理论研究中,大体上有微观和宏观两种方法。采用的是宏观的方法。利用推广的Ja-cobson方法,讨论了超导体/正常金属/半导体/正常金属/超导体结的约瑟夫逊效应,并在小电流假设下,推导出了该结的电流密度与位相之间的关系。     

直流和交流Josephson效应的研究

基于Feynman模型得到的Josephson方程,在求解过程中采取了ρ1=ρ2的假设,但这个假设在数学处理上并不严格。为了得到严格的结果,未进行上述假设,通过解微分方程得到了严格的Josephson方程,结果显示在一定条件下才能得到通常所说的Josephson方程。     

Spatially resolved gap closing in single Josephson junctions constructed on Bi_2Te_3 surface

Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators.Previously,we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi_2Te_3 surface.In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi_2Te_3 surface.     

Aspects of dissipation effects in experiments on macroscopic quantum tunnelling in Josephson junctions

Summary The effect of dissipation in experiments on macroscopic quantum tunnelling in Josephson tunnel junctions are discussed. The frequency-dependent, nonlinear dynamic resistance of the junction makes it difficult to understand which effective linear resistance has to be chosen to compare the experimental results with the theory developed in the framework of the RSJ model. Various experiments reported in the literature lead to different conclusions and are presently discussed. Recently obtained experimental results on the thermal regime allow us to propose a new experimental strategy which ultimately should remove any ambiguity on the possibility to observe MQT process in the presence of dissipation in Josephson structures. To speed up publication, the authors have agreed not to receive proofs which have been supervised by the Scientific Committee.