Showing papers by "Keiji Enpuku published in 1982"
TL;DR: In this article, the microwave response of the dc quasiparticle tunneling current in Josephson tunnel junctions is studied quantitatively in order to clarify its characteristics as a probe for the measurement of the junction capacitance.
Abstract: The microwave response of the dc quasiparticle tunneling current in Josephson tunnel junctions, where the Josephson current is suppressed by an external magnetic field, has been studied quantitatively in order to clarify its characteristics as a probe for the measurement of the junction capacitance. Extensive experiments for both small and long junctions are carried out for distinguishing between microwave behaviors of lumped and distributed constant junctions. It is shown that the observed voltage dependence of the dc quasiparticle tunneling current modified by an applied rf field is in good agreement with a theoretical result which takes into account the influence of the microwave circuit connected to the junction. The comparison between theory and experiment gives the magnitude of the internal rf field in the junction. Together with the applied rf field, this internal rf field leads to the junction rf impedance which is dominated by the junction capacitance in our experimental condition. In the case of lumped junctions, this experimental rf impedance is in reasonable agreement with the theoretical one with the junction capacitance estimated from the Fiske step of the distributed junction fabricated on the same substrate; the obtained ratio of the experimental impedance to the theoretical one is approximately 0.6–1.7. In the case of distributed junctions, however, experimental values of their characteristic impedances are approximately 0.2–0.3 of theoretical values calculated by assuming the one‐dimensional junction model and taking account of the standing‐wave effect in the junction.
4 citations
TL;DR: In this paper, an analytical solution of the Josephson equation describing the dynamic behavior of a logic gate in its resetting process is obtained with the modified averaged Lagrangian method, which is capable of quantitative discussion and is applicable to arbitrary waveforms of the gate current.
Abstract: The so‐called punchthrough phenomenon occurring in a logic gate using a Josephson tunnel junction is studied theoretically. An analytical solution of the Josephson equation describing the dynamic behavior of the Josephson gate in its resetting process is obtained with the modified averaged Lagrangian method. The solution leads to an expression for the punchthrough probability, which is capable of quantitative discussion and is applicable to arbitrary waveforms of the gate current. From the obtained expression, a study is made of the waveform dependence of the punchthrough probability, as well as its dependence on junction parameters. It is shown that the present analytical results agree well with those of computer simulations.
2 citations
TL;DR: In this paper, the velocity of a moving vortex train in long Josephson junctions is measured from the dc voltage induced by its motion by using the theory given by Scott et al. The measured velocity is strongly dependent on the amplitude of the vortex train, whose dependence is in good agreement with the theoretical result.
Abstract: The velocity of a moving vortex train in long Josephson junctions is measured from the dc voltage induced by its motion by using the theory given by Scott et al. The measured velocity of the vortex train is shown to be strongly dependent on the amplitude of the vortex train, whose dependence is in good agreement with the theoretical result.
TL;DR: In this paper, the relation between junction parameters and the oxide barrier is discussed from the change of junction parameters due to the aging effect, and a method is given to determine the distribution of the critical current density from the dc current-voltage characteristic.
Abstract: PbInAu Josephson tunnel junctions are fabricated by RF plasma oxidation procedure, and their properties are investigated quantitatively in order to diagnose junctions. From the comparison between theory and experiment of dc current-voltage characteristics, some basic parameters of the junction are obtained. The relation between junction parameters and the oxide barrier is also discussed from the change of junction parameters due to the aging effect. Futhermore, a method is given to determine the distribution of the critical current density from the dc current-voltage characteristic, and a uniformity of the oxide barrier is discussed by using this method.