Characteristics of Nb/NbOx/Al injection controlled planar three terminal superconducting devices (injection controlled links) have been studied experimentally. A built-in Nb/AlOx/Nb Josephson junction is used to perform direct tunneling measurement, whose results show that the gap in the Nb strip decreases according as its critical current is suppressed. It is also shown that the static characteristics of the devices with high and low injector resistance can be fitted to a simple heating model and a modified heating model respectively.
Characteristics of Nb/NbOx/Al injection controlled planar three terminal superconducting devices (injection controlled links) have been studied experimentally. A built-in Nb/AlOx/Nb Josephson junction is used to perform direct tunneling measurement, whose results show that the gap in the Nb strip decreases according as its critical current is suppressed. It is also shown that the static characteristics of the devices with high and low injector resistance can be fitted to a simple heating model and a modified heating model respectively.
We present Nb/AlOx/Nb–Al/AlOx/Nb stacked Josephson junctions which we propose as three-terminal elements to control the quantum behavior of Josephson complex systems. A bias current can be independently injected in the “top” junction, providing a fine control of the critical current of the “bottom” junction. The reported characterization of the device refers to data in the classical limit including measurements of the switching dynamics between metastable states of the system at different temperatures and bias conditions. At low temperature, the effective dissipation of the bottom junction remains substantially unchanged when different injection currents flow in the top junction. These results are interesting to project new configurations of macroscopic quantum experiments.
We report experimental results on characteristics of SFIFS junctions and multiterminal SFIFSIS and SISFIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlOx), and a ferromagnetic material (Ni), respectively). The SFIFS (SFIS) junctions serve as injectors in the SFIFSIS (SISFIS) devices, which have transistorlike properties; for this reason, we call them superconducting-ferromagnetic transistors. We have found the F (Ni) thickness at which the SFIFS current-voltage characteristic becomes linear. For three-terminal SFIFSIS devices, we focused on studying the influence of the injection current through the SFIFS junction on the maximum Josephson current of the SIS acceptor. For four-terminal SISFIS devices, we studied dependence of the transport current through the middle Nb electrode on injection current level through the SFIS junction. In both cases, we found that the output superconducting current (either Josephson or transport) can be efficiently modulated by the quasiparticle injection from SFIFS or SFIS input junction. The experiments indicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, digital, and RF applications.
New effects of quasiparticle injection on microwave irradiated Josephson triodes are demonstrated. The device comprises Pb-insulator (Nb2O5)-Nb SIS junction with direct contact of the Nb film to n+-GaAs gate substrate. In this device, the very thin Nb film (300 - 600 Å) as a base electrode of the SIS detector also serves as an acceptor of the quasiparticles injected from GaAs - Nb Sehottky barrier. The emphasis was placed on injections of hot quasiparticles with the energy in excess of 0.5 eV. The zeroth step height of microwave (10 GHz) irradiated Josephson current Iowas efficiently modulated by a sufficiently low density quasiparticle injection current Iinj(1 - 2 A/cm2), though no sign of change was found in the superconductive gap parameter and the Josephson critical current itself. These characteristic features became less pronounced as the energy of injected quasiparticles was lowered below 50 meV. Though the present experiment is in a preliminary stage, a current amplification (dIo/dIinj) of higher than two has been attained on a test specimen.
Interest in superconducting transistors is due to some potential benefits of these devices, such as the possibility to have large current gain and bandwidth at low temperatures. In this work we present experimental results concerning with a new superconducting 3-terminal device showing true transistor-like properties at T=4.2K. It is a stacked double tunnel junction structure where the intermediate film is a bilayer of superconducting Nb with an Al quasiparticle trap which can be either in the superconducting or in the normal metal state. Current amplification factors of up to 2.0 are observed at a temperature of 4.2 K when the Al is superconducting. When the Al is in the normal state, large current gains of more than 50 are observed. The operation is highly directional, i.e. practically no effect is observed when the roles of the injector and detector junctions are reversed. The results are explained according to the recently proposed QUAsiparticle TRApping TRANnsistor model.
Nb/Al–AlOx–Nb/Al–AlOx–Nb double-barrier three-terminal Josephson devices with a thin middle Nb/Al bilayer, which have potential for use as switching and amplifying elements in superconducting electronics, have been investigated in the stationary state by means of low-temperature scanning electron microscopy. For the devices with lateral sizes comparable with the effective Josephson penetration depth, we observed nearly homogeneous current distribution over the region common to the top and bottom junctions when the devices were biased across both the barriers in the absence of an external magnetic field. When the two junctions are biased separately, the current is concentrated at the junction edges in accordance with the behavior characteristic of distributed junctions. In an applied magnetic field, the vortex structure is confined to the area shared by both junctions when the device is biased as a whole. The experiment gives an indication that in the stationary state the spatial phase difference distribution of the two junctions coincides in the shared region at least in some interval of the external magnetic field.
We report experimental results on characteristics of SFIFS junctions and multi-terminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlOx), and a ferromagnetic material (Ni), respectively). The SFIFS junctions serve as injectors in the SFIFSIS devices which have transistor-like properties; for this reason we call them Superconducting-Ferromagnetic Transistors (SFTs). We have found the F (Ni) thickness at which the SFIFS current-voltage characteristic (CVC) becomes linear. Furthermore, we investigated the DC and AC characteristics of SFTs of two types: ordinary devices with a single acceptor (SIS) junction, and devices with a double acceptor. In the first case, we focused on studying the influence of the injection current through the SFIFS junction on the maximum Josephson current of the SIS acceptor. For devices of the second type, we studied voltage amplification properties when the operating point was chosen in the sub-gap region of the acceptor CVC. By applying an AC signal (in the kHz range) while biasing the injector (SFIFS) junction with a constant DC current, we observed a voltage gain above 25 on the double acceptor. In the reverse transmission experiment, we applied DC current and an AC modulation to the acceptor junction and, within the accuracy of the experiment, observed no response on the injector junction, which implies an excellent input-output isolation in our SFIFSIS devices. The experiments indicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, digital, and RF applications.