Properties of niobium-based Josephson tunnel junctions with a lead-indium alloy top electrode

A fabrication process for niobium-based Josephson superconductive tunnel junctions with a Pb/In alloy top electrode which showed very good mechanical and electrical properties and high oxide uniformity is described. The dependence of the junction parameters on the In-percentage in the alloy is also reported, and the results, in connection with data on the barrier composition, obtained via Auger electron-spectroscopy analysis, are discussed.     

Operation of NIST Josephson Array Voltage Standards

This paper begins with a brief discussion of the physical principles and history of Josephson effect voltage standards. The main body of the paper deals with the practical details of the array design, cryoprobe construction, bias source requirements, adjustment of the system for optimum performance, calibration algorithms, and an assessment of error sources for the NIST-developed Josephson array standard.     

Josephson effect in high-T c superconductivity

In this report we present the most important results of our recent analysis (Kupriyanov and Likharev 1990) of the Josephson effect in both the natural (intergrain) and artificial junctions using high-T _c superconductors (HTS). A comparison of the experimental data with the BCS-based theories of the Josephson effect in various tunnel-junction-type and weak-link-type structures has been carried out. The main conclusion is that the data presently available do not enable one to either confirm or reject the theories, and thus to reveal possible deviations of the real microscopic mechanism of the high-T _c superconductivity from the BCS mechanism. We suggest several experiments which would be more fruitful for this purpose, as well as for finding ways of reproducible fabrication of practically useful Josephson junctions. This work was supported by the Soviet Scientific Council on the high-Tc superconductivity problem (Grant No.42). Invited talk at the International Conference on Superconductivity, Bangalore, January 1990.     

Numerical simulation of collective phenomena in Josephson junction networks

Collective pinning phenomena of vortices in Josephson junction networks (JJN) in magnetic fields are studied using numerical simulations. We consider two kinds of structure of JJN: a ladder (Josephson junction ladder, JJL) and a two-dimensional square array (Josephson junction array, JJA). For the JJL and JJA with distribution of the strengths of junction critical currents, we investigate the critical current of vortex depinning in the presence of bias currents. On the basis of a theory of collective vortex pinning, it is found that the critical currents for both JJL and JJA show a universal scaling behavior.     

Low-cycle fatigue properties of eutectic solders at high temperatures

This paper details the deformation mechanism and low‐cycle fatigue life of eutectic solder alloys at high temperature (around 0.8T_m). Grain boundary sliding generally nucleates a wedge‐type cavity that reduces the low‐cycle fatigue life of metals. In this study, grain boundary sliding has promoted intergranular failure contributing to the reduction in fatigue life of Sn–Ag–Cu alloy. However, grain boundary sliding has exerted no deleterious effects on fatigue resistance of eutectic Pb–Sn and Bi–Sn alloys. The phase boundary sliding with very fine microstructure induces exceptional ductility in these alloys leading to superior low‐cycle fatigue endurance for theses eutectic Pb–Sn and Bi–Sn alloys.     

Periodic Properties of Voltage Versus Applied Magnetic Flux Curves in Elementary Cubic Networks of Josephson Junctions

We study the periodicity properties of a homogeneous elementary three-dimensional network of Josephson junctions in the presence of linear and shear strain of the cubic structure. We find that, for small values of the strain parameters, the system still retains periodicity in the voltage versus applied field curves. In addition, we see that these periodicities can be analytically related to the value of the period of a homogeneous and symmetric cubic network of Josephson junctions. Therefore, we argue that the system, even when subject to small structural deformations, shows robustness in the periodic behaviour of its observable electrodynamic quantities.     

Static Magnetic Flux Dynamics in One-Dimensional (1D) Josephson Lattices

We investigated static magnetic flux dynamical properties of one-dimensional lattices of Josephson junctions. The discretized wave equations of the Josephson junction lattice were solved using a generalized relaxation iteration algorithm. Numerical simulations indicated that transitions between periodic state and chaotic state will occur as the physical parameters and geometric parameters such as external current y _n, magnetic field h ₀, h, and the length of Josephson junction _n and d _n , varied. A shot length of the Josephson junction favors stable periodic states.     

Properties of niobium nitride-based Josephson tunnel junctions

High T_c (16.8 K) niobium nitride thin films have been prepared by rf diode sputtering in N₂/Ar atmosphere and subsequent high temperature annealing. Josephson tunnel junctions have been made by thermal oxidation of the films. The geometry is defined by high resolution photolithography. The Josephson junctions have been characterized by magnetic field diffraction measurements and other techniques and are shown to be particularly suitable for applications especially in superconducting microwave integrated devices.     

Microstructure control in Pb3Bi thin films for Josephson junctions

Investigation of PbBi thin films deposited by thermal evaporation was made in the range of 22–40% of bismuth. Low temperature resistivity and critical superconductive temperature depend strongly on bismuth concentration.SIMS depth profiling, X-ray diffraction and TEM analysis allow us to identify the mixture of crystallized HCPPb₃Bi phase and other surface and internal phases. Drastic oxidation effects were observed on these layers; some additional thin film materials, such as indium and SiO were deposited upon PbBi to reduce oxidation.Low leakage current, niobium-oxide-Pb₃Bi junctions were made with these alloys as counter-electrodes.     

Excitation of Josephson junction by an electromagnetic field in the nonlinear process formalism

The numerical analysis of the excitation of the Josephson junction (Jj) by an external electromagnetic field has been reported. The fully nonlinear approach requires using the quasiperiodic solutions of the sine-Gordon equation (sGe) which are expressed by the Riemann theta functions. Their local soliton approximation of the nondissipative Jj is presented. Using the self-consistent phenomenological model of a long Jj, the influence of the external electromagnetic field on the volt-ampere characteristics is considered.     

用于量子电压基准中约瑟夫森结阵列的CMP平整化工艺研究

化学机械平坦化(chemical mechanical planarization,CMP)工艺处理Si02绝缘层是一种获得高度集成化超导电路的关键技术,尤其适合于多层堆叠约瑟夫森结阵列器件的平整化.设计了应用于热氧化生长的Si02薄膜和化学气象沉积生长的Si02薄膜的CMP工艺,得出两种薄膜的抛光速率分别为2 nm/...     

Simulation of a NDRO memory cell with very small excess current Josephson junctions

The dynamic behaviour of a single flux quantum NDRO interferometer cell with two very small excess current Josephson junctions is simulated for a clamping impedance parallel to the interferometer inductance. A proper design of the clamping impedance yields the required NDRO and written operations at large damping parameters β > 1000 of the Josephson junctions. Since large damping parameters are required for logic circuits the proposed NDRO memory cell and logic circuits can now be implemented with the same fabrication process.     

Josephson effects and dc SQUID behaviour in break junction of Y-Ba-Cu-O at 77 K

Break junctions of Y-Ba-Cu-O superconductor were realized by creating fresh crack in the bar shape bulk samples mounted in a specially designed probe kept in the liquid nitrogen bath. While the bulk sample was kept static, a sharp tip of a shaft was moved downward from the outside of the dewar in order to break the sample. It was possible to change the critical current of the break junctions by adjusting pressure on the tip of the shaft. The effects of magnetic field and microwave power on the I-V characteristic of the junction were studied. The junction was found to show periodic V-B behaviour and the microwave-induced Shapiro steps were clearly observed at 77 K. The flux noise spectrum of the junction was also studied.     

约瑟夫森结Nb电极的实验研究

通过溅射Nb膜张力与氩（Ar）压强的关系，超导转变温度Tc，室温阻扰与液氮温度阻抗比RRT／RLN2，沉积中Ar浓度CAr与负偏压关系的测量和扫描电子显微镜的观察分析，对约瑟夫森结Nb电极作了研究。发现Ar压强在1．1Pa时，Nb膜呈现无应力状态；低负偏压下沉积的Nb膜晶粒结构是由致密膜到圆柱状。在偏压Ub＝－50V时，获得表面致密均匀、晶粒结构合适的Nb膜。对Nb膜用阳极氧化电压谱图（AVS）分析，证实沉积的Nb膜内不存在氧化物、寄生结和分层界面。     

The Bradbury Butterfly Effect in Long Josephson Junctions

In a well-known science fiction novel by Ray Bradbury, a butterfly in the pre-historic past is accidentally crushed by time travelers and this seemingly insignificant event radically changes history. We will call this the “Bradbury Butterfly” Effect (BBE). We know that such an effect occurs in Long Josephson Junctions as described by a time-dependent nonlinear sine-Gordon equation. This equation states that any alteration within the initial perturbation fundamentally changes the asymptotic state of the system. The actual manifestation of this effect is proven by a numerical simulation of the time-dependent sine-Gordon equation.     

SnAgCuEr系稀土无铅钎料的显微组织与性能研究

系统研究了添加微量稀土Er对Sn3.8Ag0.7Cu钎料合金显微组织和性能的影响,通过对钎料的熔化温度、润湿性能、接头剪切强度的测试及显微组织观察,指出含微量稀土的SnAgCuEr合金是性能优良的无铅钎料合金,同时确定了最佳的Er含量范围.     

Numerical Simulations of the Fluxon Dynamics of a Two-Dimensional Josephson Junction System

A direct perturbation method applied to a long Josephson junction molded by one-dimensional sine-Gordon equation is presented and the modulation of perturbations on fluxon velocity and stable state is studied. Simulations of a two-dimensional Josephson junction with dc bias current in an external magnetic field provide an I–V characteristic curve for the system and determine the various dynamic behaviors, including the periodic, quasiperiodic, and chaotic motions. Physical explanations for the behaviors are presented. The numerical results are in good agreement with the energetic analysis.     

Josephson Current in Nb/InAs/Nb Highly Transmissive Ballistic Junctions

Highly transmissive ballistic junctions are demonstrated between two superconducting Nb electrodes and the two-dimensional electron gas formed at an InAs/AISb heterojunction. A reproducible fabrication protocol is presented yielding good critical supercurrent values. Current–voltage characteristics were measured down to 0.4 K and the observed supercurrent behavior was analyzed within a ballistic model in the clean limit. This investigation allows us to demonstrate an intrinsic interface transmissivity exceeding 86%.     

Controlling Chaos in the RF-Biased Josephson Junction with Thermal Noise

In this paper the control of chaos in the rf-biased Josephson junction circuit is studied. Numerical simulation indicates that the unstable periodic orbits (UPO) embedded in the chaotic attractor can be stabilized with the delayed feedback technique. Upon controlling, operation state of the chaotic Josephson junction circuit switches back to its conventional state. Namely, phase locking is reestablished and typical I-V curve recovers. Furthermore, we investigate the influence of thermal noise on the control and estimate the range of the environmental temperature for an effective control through numerical simulation.     

我国的1V及10V约瑟夫森量子电压基准装置

文章描述了我国量子电压基准的建立、发展、现状和所取得的成果,以及与国际计量局进行基准关键比对的情况。