高温超导双晶约瑟夫森结阵列毫米波相干辐射

研究了嵌入Fabry-Perot谐振腔的高温超导双晶约瑟夫森结阵列毫米波相干辐射的实验结果.相干辐射是通过约瑟夫森结阵列与基片(作为一个介质谐振器)和Fabry-Perot(FP)谐振器的共同作用实现的.由166个高温超导双晶约瑟夫森结串联阵列在77 K温度下产生的相干辐射,辐射峰的中心频率为75.84 GHz,功率大约为10 pW. 关键词： 高温超导薄膜 Fabry-Perot谐振腔 约瑟夫森结 毫米波辐射     

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。     

嵌入Fabry-Perot谐振腔的高温超导双晶约瑟夫森结的毫米波辐照特性研究

采用嵌入Fabry-Perot谐振腔的方式,研究了Tl2Ba2CaCu2O8(Tl-2212)高温超导薄膜双晶约瑟夫森结的毫米波辐照特性.重点研究了双晶约瑟夫森结与Fabry-Perot谐振腔的耦合特性,发现放置在谐振腔中的结的位置、角度、结的图形以及Fabry-Perot谐振腔中两镜面间的距离等对耦合都有很大的影响.通过精细调节这些参数,可使双晶约瑟夫森结与外加毫米波达到最佳耦合.在最佳耦合情况下,能观察到9级明显的夏皮罗台阶.利用Fabry-Perot谐振腔技术,解决了约瑟夫森结与毫米波的耦合问题,为高温超导约瑟夫森结的毫米波及太赫兹波的辐射和检测研究奠定了基础.     

热噪声对串联约瑟夫森结阵列相位锁定的影响研究

相位锁定对于约瑟夫森结阵列的应用具有重要意义,采用数值仿真的方法研究了热噪声对约瑟夫森结阵列相位锁定的影响。采用电阻电容并联约瑟夫森结模型,利用公共并联电阻实现阵列的相位锁定,取不同的热噪声水平研究系统存在相位锁定的参数范围。结果包括不同热噪声情况下,约瑟夫森结临界电流的不一致性、McCumber参数对实现相位锁定的参数范围的影响,得到了热噪声对相位锁定的影响规律。     

并联电阻对串联约瑟夫森结阵列相位锁定的影响研究

利用约瑟夫森结阵列制作毫米/亚毫米微波源的一个重要问题是阵列中约瑟夫森结的相位锁定.本文采用仿真的方法研究了约瑟夫森结RCSJ模型存在并联电阻时的相位锁定问题.研究结果包括约瑟夫森结临界电流的不一致性、McCumber参数和结的个数对能够实现相位锁定的参数范围的影响.结果对于约瑟夫森结阵列作为太赫兹产生和检测应用具有重要意义.     

SrTiO3基片上Tl-2212双晶约瑟夫森结的动态特性及噪声影响研究

在SrTiO₃（STO）基片上制作了Tl-2212双晶约瑟夫森结,并对其进行了微波辐照下的I-V特性测试,观察到了夏皮罗台阶,符合约瑟夫森电压-频率关系.利用数值仿真对约瑟夫森结建立了RCSJ模型,仿真结果与实验数据符合较好,利用此模型深入研究了噪声对结动态特性的影响,解释了噪声影响下结的微波感应台阶幅度减小和极小值展宽现象,提出了有效噪声温度为工作温度和外部噪声的等效温度之和. 关键词： RCSJ模型 噪声 Tl-2212双晶约瑟夫森结     

利用一种改进模型研究谐振器耦合时的约瑟夫森结的响应(英文)

提出了一种改进的谐振器耦合时的约瑟夫森结模型,模型考虑了结与谐振器之间的耦合强度。利用这种模型,研究了谐振器耦合时的约瑟夫森结的响应,包括单结的电压自锁定和结阵列的相位互锁定现象。研究了耦合强度、谐振器的品质因数和谐振频率对电压自锁定的影响,并给出了合理的解释。此外,还对结阵列的相位互锁定强度对锁定电压和结数量的依赖关系进行了研究,并与理论值进行了比较。所得结果对谐振器耦合下的约瑟夫森结的应用具有指导意义。     

约瑟夫森结(阵列)与谐振器的耦合效应研究

利用一种新的电路模型系统研究了约瑟夫森结(阵列)与谐振器的耦合效应.以结的电压自锁定台阶幅度ΔI为目标值,得到了谐振电路的电阻R、谐振频率fr对耦合的影响规律,并给出了合理解释;以结阵列的相位互锁定强度IL为目标,研究了IL对锁定电压VL的依赖关系,同时,通过相关计算将其与通常电路模型下得到的结果进行了比较.     

SNS与SINIS结阵制作工艺的比较

国家电压基准是基于约瑟夫森量子化效应的。传统的SIS结阵具有不能快速选择特定的台阶,相位锁定时间短的问题。I-V曲线无回滞的约瑟夫森结阵,其I-V曲线单值,电压台阶宽,解决了SIS结阵的问题。美国标准技术研究院的Hamilton提出并制作高度阻尼的可编程SNS约瑟夫森结阵电压标准;德国物理技术研究院则选择SINIS结来制作可编程约瑟夫森结阵电压基准。从结构、性能和制作方法等方面对SNS和SINIS可编程约瑟夫森结阵进行了比较。     

光纤Fabry-Perot谐振腔的精细度对相位灵敏度的影响

分析了光纤Fabry-Perot谐振腔的工作原理及其工作点的选择问题，推导了谐振腔的光学相位灵敏度与精细度的关系，给出了理论公式及曲线，并与光纤Math-Zehnder干涉进行了对比，指出了在相位灵敏度上两者的巨大差距，证明了光纤Fabry-Perot干涉的独特优点.介绍了光纤Fabry-Perot干涉的实验系统，提出了检测及计算Fabry-Perot谐振腔有效精细度的方法，实验结果与理论仿真基本吻合.     

Self-radiation from arrays of niobium Josephson junctions embedded in the open resonator

This paper focuses on self-radiation from arrays of Josephson junctions embedded in a quasi-optical resonator. The mechanism of coupling this radiation to the principal mode of the open resonator is illustrated using experiments and simulations with CST microwave studio software. Comparing the microstrips and dielectric resonators used as the antennas of the series arrays of discrete Josephson junctions, we demonstrate that the dielectric resonator antennas are more effective than microstrips.     

Design optimization for microwave coupling structures of a digital-to-analog converter based on series arrays of high-temperature superconducting Josephson junctions

A new coupling scheme of the external microwave signal for a digital-to-analog converter based on series arrays of high-temperature superconducting Josephson junctions has been proposed. It is suggested to couple the meander-like array inductively to a parallel microwave transmission line. Within the resistively shunted junction model different types of microwave coupling structures were analyzed with the goal to reduce the mutual phase locking and to achieve high output power and phase-locking stability. A harmonic balance technique was used to derive an analytic expression connecting the amplitudes of microwave voltages and currents in the array and the frequency of the external signal. Numerical simulations were performed to determine the boundaries of stable locking as a function of circuit parameters.     

Simulation and measurement of millimeter-wave radiation from Josephson junction array

We report the circuit simulations and experiments of millimeter-wave radiation from a high temperature superconducting(HTS) bicrystal Josephson junction(BJJ) array. To study the effects of junction characteristic parameters on radiation properties, new radiation circuit models are proposed in this paper. The series resistively and capacitively shunted junction(RCSJ) models are packaged into a Josephson junction array(JJA) model in the simulation. The current-voltage characteristics(IVCs) curve and radiation peaks are simulated and analyzed by circuit models, which are also observed from the experiment at liquid nitrogen temperature. The experimental radiation linewidth and power are in good agreement with simulated results. The presented circuit models clearly demonstrate that the inconsistency of the JJA will cause a broad linewidth and a low detected power. The junction radiation properties are also investigated at the optimal situation by circuit simulation. The results further confirm that the consistent JJA characteristic parameters can successfully narrow the radiation linewidth and increase the power of junction radiation.     

Synchronization of underdamped Josephson-junction arrays

Our recent experiments show that arrays of underdamped Josephson junctions radiate coherently only above a threshold number of junctions switched onto the radiating state. For each junction, the radiating state is a resonant step in the current-voltage characteristics due to the interaction between the junctions in the array and an electromagnetic cavity. Here we show that a model of a one-dimensional array of Josephson junctions coupled to a resonator can produce many features of the coherent be havior above threshold, including coherent radiation of power and the shape of the array current-voltage characteristic. The model also makes quantitative predictions about the degree of coherence of the junctions in the array. However, in this model there is no threshold; the experimental below-threshold region behavior could not be reproduced.Received: 11 April 2003, Published online: 23 July 2003PACS: 74.50.+r Tunneling phenomena; point contacts, weak links, Josephson effects - 85.25.-j Superconducting devices