The new BIPM 1-V reference standard based on an array of Josephsonjunctions

The authors report the first measurements at the Bureau International des Poids et Mesures (BIPM) with a 1-V reference standard based on an array of Josephson junctions. A novel procedure for standard cell measurements is described. It allows the measurement of a cell electromotive force (EMF) with a random uncertainty of less than 1 nV and a total uncertainty of about 2 nV while avoiding direct connection of the cell to the array. Comparisons with an older Josephson reference standard, which is based on a junction output of 10 mV, were made both indirectly by means of standard cells and directly by connecting the instruments together. The results and the random uncertainties imply that the value assigned to a standard cell using the array minus that given by the older apparatus is -18.8±3.4 nV for the indirect method and -17.1±1.5 nV for the direct method. Taking into account the estimated total uncertainty of 23.5 nV for the old system, the agreement is excellent     

Josephson parameters of bicrystal junctions of a new type based on metal oxide semiconductors

We have studied symmetric bicrystal Josephson junctions of a new type based on metal oxide superconductors in which the base planes are misoriented relative to the [100] direction by an angle within 22°–28°. These junctions exhibit record high values of the critical parameters at T = 77 K: the critical current density reaches I _C = (2−5) × 10⁵ A/cm² and the characteristic voltage is V _C = I _C R _N = 0.6−0.9 mV. The properties of the new junctions have been determined for the first time under the influence of monochromatic microwave radiation in the millimeter wavelength range and have been studied as functions of the magnetic field and temperature. The observed dependences of the critical current and the Shapiro step height on the electromagnetic field amplitude agree well with the theoretical predictions according to the resistive shunted junction model of the Josephson junction. The new junctions can be used in real superconducting devices operating at liquid nitrogen temperatures.     

Metal oxide bicrystal Josephson junctions of a new type with high critical parameters

Film bicrystal Josephson junctions of a new type based on a metal oxide high-T _c superconductor of the YBa₂Cu₃O_7−x (YBCO) system are suggested and studied. In junctions of the new type, in contrast to the known ones, the working surfaces situated on the opposite sides of the bicrystal interface have different crystal orientations: one is (001)YBCO, and the other is rotated (misoriented) relative to it by an asymmetric bicrystal angle around a certain axis lying in the substrate plane. The main electrical and dynamic (microwave) characteristics have been determined for junctions of the new type based on NdGaO₃ bicrystal substrates with the misorientation angle varying from 13° to 28°. These junctions exhibit high values of the critical parameters at T=77 K, including the critical current density I _C= (2–5)×10⁵ A/cm² and the characteristic voltage V _C=I _C R _N=0.6–0.9 mV. Advantages of the bicrystal Josephson junctions of the new type over the known junctions are considered.     

Report on international comparison of power at 94 GHz

An international comparison of power standards at 94 GHz was approved at the 1983 meeting of the Radio Frequency Working Group of the Consultative Committee on Electricity, Participants in the comparison were ETL (the pilot laboratory, Japan), LCIE (France), NIST (US), and RSRE(UK). Three thermistor mounts as the transfer standards were circulated among the participants, who measured the effective efficiencies of the mounts. Relative deviations in power measurements at 94 GHz by the participants lie within a range of 1.3%     

Direct comparison of two independent Josephson voltage standards at1 V and precision measurements up to 10 V

Two Josephson voltage standards have been compared using a room-temperature electronic nanovoltmeter with a peak-to-peak noise of about 2 nV at the 1-V level corresponding to a RMS uncertainty of 4×10^-10. The excellent stability in maintaining the desired voltage steps makes it possible to obtain recorder traces comparing Nb/Al₂O₃/Nb Josephson standards with Weston cells and Zener reference standards at 1 V and 10 V. At 10 V the best result shows a peak-to-peak noise of 250 nV corresponding to a RMS uncertainty of 5×10^-9 for a Zener reference and 50 nV corresponding to 1×10^-9 for a series connection of nine Weston cells. As an example for the application of the Josephson standard as a potentiometer the deviation in the linearity of a digital voltmeter is confirmed to be on the order of 0.1 p.p.m. in the range from -10 V to +10 V     

High-power InP/GaInAsP buried heterostructure semiconductor laser with a modulation band of up to 10 GHz

As a continuation of our studies aimed at designing InP/GaInAsP heterostructures based on semi-conductor solid solutions, we consider the design and fabrication aspects of laser emitters with a high average-power bandwidth product. We describe in detail experimental studies of the microwave parameters of laser emitters and present their power-current curves, spectral response, and frequency modulation characteristics at frequencies of up to 10 GHz.     

A biosensor array based on polyaniline

This paper describes the fabrication of polyaniline-based microsensors and microsensor arrays for the estimation of glucose, urea, and triglycerides. Microelectronics technology has been used to produce gold interdigitated microelectrodes on oxidized silicon wafers. Polymer deposition and enzyme immobilization has been done electrochemically. Electrochemical potential control has been used to direct enzyme immobilization to the chosen microelectrodes and prevent it at other microelectrodes in contact with the enzyme solution. This has enabled the immobilization of three different enzymes on three closely spaced microelectrodes, resulting in a sensor array which can analyze a sample containing a mixture of glucose, urea, and triolein in a single measurement using a few microliters of the sample. This strategy is quite general and can be extended to other enzyme-substrate systems to eventually produce an "electronic tongue".     

Characteristics of series-connected chains of YBaCuO Josephson junctions on a bicrystal substrate

An investigation was made of the electrophysical characteristics of chains of high-temperature superconducting Josephson junctions on a bicrystal substrate. Their interaction with millimeter radiation was also studied. It was shown that these chains can be used to detect millimeter and submillimeter radiation. Pis’ma Zh. Tekh. Fiz. 24, 83–89 (December 26, 1998)     

Dynamics and phase transitions of Josephson junctions with dissipation due to quasiparticle tunneling

We investigate the dynamics and the phase diagram of Josephson junctions where the dissipation is due to quasiparticle tunneling. This system is formally equivalent to a one-dimensional X-Y model with easy axis and long-range interaction. It has a phase transition at a critical strength of the dissipation, which differs in several respects from the one encountered if the dissipation is Ohmic. Quantum effects are reduced, though not destroyed, above this transition. We discuss the response of a junction to an imposed current. In the linear regime Coulomb blockade is important; in the nonlinear regime under suitable conditions Bloch oscillations can occur.     

Comparison of a Multichip 10-V Programmable Josephson Voltage Standard System With a Superconductor–Insulator–Superconductor-Based Conventional System

We developed a 10-V dc programmable Josephson voltage standard (PJVS) using a multichip technique. The PJVS was based on $hbox{NbN/TiN}_{x}/hbox{NbN}$ junctions and operated using a 10-K compact cryocooler. We carried out an indirect comparison with a superconductor–insulator–superconductor-based conventional Josephson voltage standard (JVS) by measuring the voltage of a 10-V zener diode reference standard. The combined standard uncertainty of the comparison was $u_{c} = 0.03 muhbox{V}(k = 1)$, and the relative combined standard uncertainty was $3 times 10^{-9}$.      

A new type of biepitaxialc-axis tilted YBCO Josephson junction

A novel fabrication procedure of high critical temperature superconductor Josephson junctions (HTCSJJ) has been developed by a 90° rotation of YBa₂Cu₃O_7?x c-axis around an in-plane direction, on the basis of concepts of the biepitaxial technique. YBa₂Cu₃O_7?x grows oriented along (001) direction on a MgO seed layer deposited on a (110) SrTiO₃ substrate and along (110) direction on the bare substrate. Josephson junctions of good quality were obtained exhibiting RSJ behavior and features characteristic of HTCSJJ phenomenology. Even if not uniform, in some samples, the nature of the critical currentI _c is completely Josephson, as resulting from theI _c dependence on the applied magnetic field. The maximum measuredI _c R _N value atT=4.2K is 2mV.     

The effect of alternating current on the plasma frequency of the tunnel Josephson junctions

The effect of alternating current on the plasma frequency of the tunnel Josephson junctions simultaneously carrying both direct (dc) and alternating (ac) currents has been studied. The presence of the ac component leads to a decrease in the plasma frequency. An analytical expression describing the plasma frequency as a function of the ac current amplitude is proposed. The obtained results agree with the recent experimental data on the properties of tunnel Josephson junctions.     

A fiber optic phase modulator with an optical frequency shift of up to 20 GHz

A fiber optic phase modulator is described in which the phase of a light wave traveling in an optical fiber is modulated by a composite electromechanical resonator with Q≌1000. The instantaneous frequency of the wave at the modulator output varies according to a harmonic law. The interval of tuning of the instantaneous light wave frequency achieved in the experiment is 20 GHz, which corresponds to a modulation index of ≌10⁶. It is demonstrated that a maximum value of the frequency tuning range is determined by the elastic limit of the resonator material.     

Phase dependence of the superconducting current in YBCO Josephson junctions on a bicrystal substrate

Dependences of the amplitudes of the harmonic and subharmonic Shapiro steps on an external monochromatic signal were used to study the current-phase dependence of high-temperature superconducting junctions on a bicrystal substrate. It is shown that for a symmetric definition of the transport current across the junction with an edge transparency of the order of and a mirror-symmetric bicrystal interface, the current-phase dependence is close to sinusoidal which differs from the theoretical predictions and is most likely caused by twinning of the high-temperature superconducting films of the electrodes forming the junction. A departure from symmetry in the definition of the transport current across the junction causes the current-phase dependence to deviate from sinusoidal, which increases with increasing degree of asymmetry. This change in the current-phase dependence is accurately described by a model which takes into account the formation of coupled Andreev states in junctions of superconductors with a type of superconducting wave function. Pis’ma Zh. Tekh. Fiz. 25, 65–72 (November 26, 1999)     

The effect of alternating current on the thermal activation threshold of the tunnel Josephson junctions

The process of thermal activation in the tunnel Josephson junctions simultaneously carrying both constant (dc) and alternating (ac) currents has been studied. The presence of the ac component leads to a decrease in the potential barrier for a metastable state of the Josephson junction. The thermal activation threshold is expressed as a function of the ac current amplitude. The results agree with the data of recent experiments on the statistics of switching from a superconducting to resistive state in the Josephson tunneling junctions.     

A functional polymeric material based on hybrid electrochemically controlled junctions

A thin film polymeric junction was fabricated which yields a molecular electronic device functionally able to learn, i.e. to respond coherently to an external training signal. The fabricated structure is based upon electrochemical control of electronic current in a conducting polymer in contact with a solid electrolyte polymer. This functional behavior bears some resemblance to simple cases of biological learning processes. We report a comprehensive electronic characterization of the device function. Additional study was performed in order to estimate the possibility of the integration of such kinds of devices in statistical adaptive networks.     

A new type of biepitaxialc-axis tilted YBCO Josephson junction

A novel fabrication procedure of high critical temperature superconductor Josephson junctions (HTCSJJ) has been developed by a 90° rotation of YBa₂Cu₃O_7–x c-axis around an in-plane direction, on the basis of concepts of the biepitaxial technique. YBa₂Cu₃O_7–x grows oriented along (001) direction on a MgO seed layer deposited on a (110) SrTiO₃ substrate and along (110) direction on the bare substrate. Josephson junctions of good quality were obtained exhibiting RSJ behavior and features characteristic of HTCSJJ phenomenology. Even if not uniform, in some samples, the nature of the critical currentI _c is completely Josephson, as resulting from theI _c dependence on the applied magnetic field. The maximum measuredI _c R _N value atT=4.2K is 2mV.     

Near-Zero Bias Arrays of Josephson Tunnel Junctions Providing Standard Voltages up to 1 V

Josephson voltage standards utilize microwave-induced constant voltage steps occurring due to the ac Josephson effect. Existing standards can be considerably simplified and their accuracy improved by using a large number of series-connected Josephson tunnel junctions which are operated in the zero current step mode. For this purpose superconducting millimeter wave integrated circuits have been designed, fabricated, and tested. The circuits consist of a broadband taper between the rectangular waveguide and the planar structure, the Josephson junction series, a well-matched load, and dc pads. Circuits with various numbers of junctions have been fabricated by photo-lithographic techniques and tested at 4.2 K in liquid helium. The version with 1474 junctions produced voltages up to 1.2 V when operated at 90 GHz.     

A p-adaptive scaled boundary finite element method based on maximization of the error decrease rate

This study enhances the classical energy norm based adaptive procedure by introducing new refinement criteria, based on the projection-based interpolation technique and the steepest descent method, to drive mesh refinement for the scaled boundary finite element method. The technique is applied to p-adaptivity in this paper, but extension to h- and hp-adaptivity is straightforward. The reference solution, which is the solution of the fine mesh formed by uniformly refining the current mesh, is used to represent the unknown exact solution. In the new adaptive approach, a projection-based interpolation technique is developed for the 2D scaled boundary finite element method. New refinement criteria are proposed. The optimum mesh is assumed to be obtained by maximizing the decrease rate of the projection-based interpolation error appearing in the current solution. This refinement strategy can be interpreted as applying the minimisation steepest descent method. Numerical studies show the new approach out-performs the conventional approach.