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.     

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。     

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     

高温超导双晶结混频器噪声系数测量

噪声系数(Noise Figure,NF)是超导混频器的一个重要参数,是衡量超导混频器内部噪声、影响混频器灵敏度的一个重要指标.实验基于小型脉冲管制冷系统,搭建高温超导约瑟夫森双晶结混频器噪声系数自动测量系统,工作温度为60K.Ar离子刻蚀工艺技术制备高温超导YBa2Cu3O7-δ(YBCO)/MgO约瑟夫森双晶结,通过Y-因子噪声测量法,测量YBCO/MgO约瑟夫森双晶结混频器的噪声系数.实验成功制备了特征电压约1mV的YBCO/MgO约瑟夫森双晶结,在650GHz信号辐照下,有明显的夏皮罗(Shapiro)台阶.在210GHz信号辐照下,进行30次谐波混频,约瑟夫森双晶结在不同偏置电压点中频输出信噪比变化范围约为30dB.在77K与300K不同输入噪声功率下,测得双晶结混频器噪声系数最小值为10dB,偏置电压在300μV.     

转角铜氧化物中的约瑟夫森效应

当前常压下超导转变温度最高的材料仍然来自铜氧化物家族.然而,铜氧化物超导的微观机理仍未被完全建立起来,成为了凝聚态物理领域最具挑战性的问题之一.测定配对波函数的相位部分是全面理解高温超导机理不可或缺的一环.该实验往往需要将不同晶向的铜氧化物拼接成高质量的约瑟夫森结,十分考验样品的合成制备技术.近年来,利用二维材料中发展起来的范德瓦耳斯堆垛技术,研究者们构建了具有原子级平整界面的转角铜氧化物双晶结,研究了不同掺杂浓度、不同转角下的约瑟夫森隧穿,探索了其中出现s波、d波、以及由于界面耦合演生出的d+id波配对的可能性.本文将回顾转角铜氧化物约瑟夫森结的研究进展,介绍近年来发展起来的转角结制备技术,讨论当前实验测量的结果及其意义,提出尚待解决的关键性问题.     

高温超导约瑟夫森结太赫兹混频系统

在小型脉冲管制冷机（工作温度约60 K）上搭建了高温超导约瑟夫森结太赫兹谐波混频系统,并采取了一系列措施增强结与太赫兹波的耦合。所采取的措施主要有:研究不同基片对结的影响并最终选择MgO做为双晶结基片,设计平面周期对数天线,同时使用一个超半球硅透镜和两个离轴抛物面反射镜组成准光学系统。最终成功在小型脉冲管制冷机中获得结对623 GHz太赫兹波的响应,并且成功进行24次谐波混频实验。     

高温超导约瑟夫森结技术及其应用

高温超导约瑟夫森结技术近年来发展很快,特别是台阶结、双晶结、双外延结、边缘结和邻近效应结等性能已达到实用水平,并应用于超导量子干涉器件、数字信号处理和高频有源器件中。文章介绍了这些结的技术和有关的应用。     

基于高温超导本征约瑟夫森效应的新型两端恒流器件

我们利用高温超导本征约瑟夫森效应,研制了一种超导薄膜两端恒流器件.恒流器件是将生长在斜切20度LaAlO3基片上的Tl-2212超导薄膜光刻成微桥得到的.对于6μm×8μm的微桥器件,其最高工作电压可达15V以上,当两端电压在1V～11V之间变化时,电流基本稳定在4.3mA,误差不超过±5%,动态内阻大于104 Ω,在最佳工作位置(3V～8V)动态内阻可以达到105 Ω.通过数字模拟,对实际应用中两端恒流器件的rf调制进行了较详细的分析,并可使恒定电流上rf调制小于1%.     

高温超导约瑟夫森结太赫兹混频系统

在小型脉冲管制冷机（工作温度约60 K）上搭建了高温超导约瑟夫森结太赫兹谐波混频系统,并采取了一系列措施增强结与太赫兹波的耦合。所采取的措施主要有：研究不同基片对结的影响并最终选择MgO做为双晶结基片,设计平面周期对数天线,同时使用一个超半球硅透镜和两个离轴抛物面反射镜组成准光学系统。最终成功在小型脉冲管制冷机中获得结对623 GHz太赫兹波的响应,并且成功进行24次谐波混频实验。     

Anisotropy of p-wave Josephson junction

<正>The anisotropy of the dc Josephson current in the superconducting junctions of the p-wave equal spin pairing symmetry is theoretically investigated by the Furusaki-Tsukada-like formula.The current phase relations exhibit different oscillation periods and different phase shifts for the current along different directions,respectively.     

Ac Josephson effect in Corbino-geometry Josephson junctions constructed on Bi2Te3 surface

Recently, a Corbino-geometry type of Josephson junction constructed on the surface of topological insulators has been proposed for hosting and braiding Majorana zero modes. As a first step to test this proposal, we successfully fabricated Corbino-geometry Josephson junctions (JJs) on the surface of Bi₂Te₃ flakes. Ac Josephson effect with fractional Shapiro steps was observed in the Corbino-geometry JJs while the flux in the junction area was quantized. By analyzing the experimental data using the resistively shunted Josephson junction model, we found that the Corbino-geometry JJs exhibit a skewed current—phase relation due to its high transparency. The results suggest that Corbino-geometry JJs constructed on the surface of topological insulators may provide a promising platform for studying Majorana-related physics.     

Characteristics of the Surface-Intrinsic Josephson Junction

During the fabrication of intrinsic Josephson junctions (IJJs) with Bi₂Sr₂CaCu₂O_8+δ (BSCCO) single crystals, the superconductivity of the surface Cu-O layer is degraded because of a deposited metal film on top of the stack. Thus, the characteristics of the surface junction consisting of the surface Cu-O double layers remarkably differ from those of the junctions deep in the stack, which will be referred to as ordinary IJJs. The electrical transport characteristics of the surface junction, such as I-V, I _c′-T, and R-T, show that the critical temperature T _c′ of the surface junction is always lower than that of ordinary IJJs, and that the change of its critical current I _c′ with temperature is different from that of ordinary IIJs. Furthermore, by shunting the surface junction resistively, we are able to observe the AC Josephson effect at 3-mm waveband. Translated from Chinese Journal of Low Temperature Physics, 2005, 27(2) (in Chinese)     

约瑟夫森结在射频辐照下的亚谐波台阶仿真研究

利用PSp ice软件,采用电路仿真的方法深入研究了约瑟夫森结在射频辐照下的I-V特性,观察到了亚谐波台阶的存在,得出了台阶高度与射频电流幅度的关系,结果对于约瑟夫森结在电压标准和射频检测等方面的应用有重要的参考价值。     

Fluctuation power spectrum of a Josephson junction

The fluctuation power spectrum of the Josephson junction has been evaluated in the limit of large energy barriers [(U _n ^max−U _n ^min)γ]≫1 and small currents [x≪x _e]. The result is valid for finite capacitance of the junction. The effect of the fluctuating Josephson current on the voltageV(t) across the junction has also been taken into account.     

热噪声对约瑟夫森结I-V特性及微波感应台阶的影响研究

采用数值仿真的方法研究了热噪声对约瑟夫森结I-V特性及微波感应台阶的影响。研究表明,热噪声导致约瑟夫森结的I-V特性曲线呈现"圆拱化",也使得微波感应台阶高度减小。得出了取不同约瑟夫森结临界电流和结电阻时,热噪声对台阶的影响规律     

Effect of transparency on Josephson junction between s+g-wave superconductors

In this paper, a dc Josephson junction between borocarbide superconductors has been studied theoretically. The s+g-wave pairing symmetry which is observed in rare earth complex of borocarbides has a huge anisotropy and is an interesting form of unconventional superconductivity. We calculate the Josephson current in a superconductor--insulator--superconductor (SIS) Josephson junction with s+g-wave superconducting pairing symmetry. In our planar junction c-axis is parallel to an interface with finite transparency but ab-planes of two tetragonal superconductors are misorientated by angle α. We obtain that the Josephson current is strongly dependent on mis-orientation between the left and the right ab-planes. An insulator sandwiched between two superconductors which acts as a potential barrier is demonstrated by a transparency coefficient. The effects of the potential barrier and the mis-orientation on the current are studied analytically and numerically. Occurrence of 0--π transition in this s+g-wave junction is investigated in this paper. A comparison between d-wave Josephson junction and s+g-wave one is also made in the present paper.