Showing papers by "Keiji Enpuku published in 1984"

Flux-flow-type Josephson oscillator for millimeter and submillimeter wave region. II. Modeling

Abstract: A theoretical study is made of a travelling‐wave‐type oscillator, which utilizes a flux flow in a long Josephson junction for use as a local oscillator in the integrated superconducting receiver system. An internal electromagnetic field of the oscillator junction in the flux‐flow state is investigated both numerically and analytically. It is shown that the voltage amplitude of the internal oscillation increases gradually in the direction of the flux flow and reaches a maximum value at the junction end. An equivalent circuit of the oscillator is also obtained, which gives dependences of the emitted radiation on frequency, magnetic field, and load. It is shown that the output power attains the value of the order of 10−6 W in the frequency range between 100 and 500 GHz, and that the output power and the radiation frequency can be controlled by both the bias voltage and the applied magnetic field. These theoretical results explain quantitatively the experimental ones with a Pb‐alloy long junction of length 24 λJ.

Magnetic-flux trapping characteristics of thin-film Pb alloys as electrodes of Josephson junctions

Abstract: Magnetic‐flux trapping characteristics of thin‐film Pb alloys including Au and Bi are studied experimentally, which are used for Josephson junction integrated circuits. The amount of the magnetic flux trapped in thin‐film Pb alloys is estimated from the measurement of the quasiparticle‐current increment of Josephson junctions, which are fabricated with Pb alloys as junction electrodes. An array of Josephson junctions is used in order to observe the spatial distribution of the magnetic‐flux density in thin films. The observed magnetic‐flux behavior in thin films was apparently similar to that in nonideal bulk type‐II superconductors; magnetic‐flux distribution was similar to that expected from the so‐called pinning model, and surface barrier became large in weak magnetic fields. From the analysis of the observed data, the parameter characterizing the degree of flux trapping has been obtained, with which effects of Au and Bi on flux trapping are evaluated quantitatively. It was shown that the addition of Au...

Josephson ndro memory cell with a direct-coupled sense gate.

Abstract: Nouveau type de memoire morte a lecture non destructive Josephson, ou le circuit de lecture est couple directement a la partie memoire. La cellule de memoire fonctionne sans la complexite des sequences des signaux et la marge de fonctionnement est d'environ ±20%

Flux-Trapping Characteristics of Pb-alloy Superconducting Thin Films for Josephson Tunnel Junctions

Abstract: Magnetic-flux trapping in Pb-alloy thin films is studied experimentally. In order to clarify pinning characteristics of thin films, which dominate flux trapping, trapped flux in Pb-alloy thin films is measured in-situ from the increment of the quasiparticle current of the Josephson junction made of these Pb-alloy thin films. Experimental results are discussed with the critical state model based on the pinning theory of superconductors. From the material dependence of flux trapping, it is shown that the addition of Au to Pb increases flux trapping due to the occurence of strong pinning centers of normal precipitates of AuPb2 and AuPb3 etc. It is also shown that the addition of Bi decreases flux trapping due to the large value of the London penetration depth of PbBi films. From the temperature dependence of flux trapping, it is shown that the amount of the trapped flux is reduced by raising the temperature of thin films. Finally, the effect of the trapped flux in junction electrodes on the suppression of the critical current of the junction is discussed quantitatively.