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Journal of Applied Physics

Possible analog gain in a current injection Josephson network

Juran Chandra Biswas, Sanjoy Roy

Published Mar 15, 1986• 0 citations
Publisher

Abstract

A possible analog gain in Cooper-pair tunneling mode in a current injection Josephson network is theoretically investigated. The network consists of three Josephson junctions A, B, and C, and its gain can be widely controlled by varying the external shunt resistances of junctions B and C. Two different configurations of the planar structure of the network are suggested and their detailed principles of operation are explained. It is expected that the network will function at a higher speed than that possible in an amplifying device working in quasiparticle mode. A comparison between the present network and Faris QUITERON is also given.

DOI
10.1063/1.336396

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•Nov 9, 2004•0 citations
A possible analog gain in Cooper-pair tunneling mode in a current injection Josephson network is theoretically investigated. The network consists of three Josephson junctions A, B, and C, and its gain can be widely controlled by varying the external shunt resistances of junctions B and C. Two different configurations of the planar structure of the network are suggested and their detailed principles of operation are explained. It is expected that the network will function at a higher speed than that possible in an amplifying device working in quasiparticle mode. A comparison between the present network and Faris QUITERON is also given.
A Josephson tunnel junction transistor based on quasiparticle injection is proposed. Its operation relies on the manipulation of the electron distribution in one of the junction electrodes. This is accomplished by injecting quasiparticle current through the junction electrode by two additional tunnel-coupled superconductors. Both large supercurrent enhancement and fast quenching can be achieved with respect to equilibrium by varying quasiparticle injection for proper temperature regimes and suitable superconductor combinations. Combined with large power gain, this makes the device attractive for applications where reduced noise and low-power dissipation are required.
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This paper concerns a new three terminal superconducting weak link device, having a third electrode attached to the weak link part for injecting quasiparticles. The structure, the fabrication procedure and the result of the measurement of its static I-V characteristics are presented. As a result, a current gain larger than that of any other Josephson switching devices is obtained. It is found that the larger current gain depends strongly upon the input resistance between the third electrode and the weak link part. The switching speed of the device is also theoretically discussed.
It has long been recognized that a control current Ia injected into the section of a two- junction superconducting quantum interference device is able to produce a change of its critical current Ic, so that a current gain g = |dIc/dIa| can be identified. We investigate the circumstances under which large gains can be achieved by using vertical Josephson interferometers, which are characterized by small loop inductances. We discuss the theory of operation of such a device, its performances, and its advantages with respect to planar interferometers used in the previous works. Two potential applications are addressed.
Properties of weak links between two superconductors, or Josephson junctions, make them interesting for fundamental physics research. Since their discovery over four decades ago, they have provided a unique way to study the behavior of the superconducting quantum phase. More recently, ultra small, or mesoscopic, Josephson junctions with substantial single Cooper pair charging energy have gained interest due to their behavior as macroscopic quantum objects. In addition to the theoretical interest, Josephson junctions can be used as active elements in circuit applications. Particularly, in this Thesis we study two different devices. We develop the required theoretical treatments, derive device properties, and compare the results with experimental data. The first application is a Josephson voltage standard based on externally damped Superconductor - Insulator - Superconductor junctions. It consists of an array of large Josephson junctions connected in series and irradiated with a 70 GHz microwave signal. Phase locking the Josephson dynamics into the signal leads to the quantization of the voltage. This is utilized in metrology. We introduce a new circuit solution based on frequency dependent damping of the junctions. Optimization and some designs for practical arrays are presented. The purpose is to find such a design that the array is fast, has low power consumption and is as stable as possible. Arrays able to generate DC voltages of order 1 volt with metrological accuracy are demonstrated experimentally and their applicability in AC voltage calibrations is analyzed. The second application is the Bloch Oscillating Transistor (BOT). The BOT is based on controlling the Cooper pair current in an ultra small Josephson junction by means of quasiparticles tunneling through a normal junction. As part of the thesis work, the principle of operation is first demonstrated computationally. The model is then refined to yield quantitative predictions of the characteristics. Finally, an analytic theory for the device is developed and the properties as an amplifier are derived.