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Applied Physics Letters

A superconducting transistorlike device having good input-output isolation.

Ivan P. Nevirkovets

Published Aug 3, 2009• 16 citations
Publisher

Abstract

A multiterminal superconducting device with the S1IS2FIS3 structure (where S, I, and F denote a superconductor, an insulator, and a ferromagnetic material) is fabricated and characterized. Introducing a thin ferromagnetic layer into the middle electrode dramatically reduces parasitic back action of the acceptor junction (S1IS2) bias current on the injector junction (S2FIS3) current-voltage characteristic as compared with that for the formerly reported quiteron, a device exploiting similar operation principle.

DOI
10.1063/1.3189283

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IEEE Transactions on Applied Superconductivity•Jan 12, 2015•24 citations
A multiterminal superconducting device with the S1IS2FIS3 structure (where S, I, and F denote a superconductor, an insulator, and a ferromagnetic material) is fabricated and characterized. Introducing a thin ferromagnetic layer into the middle electrode dramatically reduces parasitic back action of the acceptor junction (S1IS2) bias current on the injector junction (S2FIS3) current-voltage characteristic as compared with that for the formerly reported quiteron, a device exploiting similar operation principle.
A new design for a multi-terminal superconducting transistor-like device exploiting tunnelling injection of quasiparticles is proposed, in which parasitic back-action of the acceptor junction (S1IS2) bias current on the injector junction (S2FIS3) current–voltage characteristic (CVC) is dramatically reduced as compared with that for the formerly reported quiteron (here S, I, and F denote a superconductor, an insulator and a ferromagnetic material). Improvement of the isolation is achieved owing to the short electron mean free path and short coherence length in a thin F layer that screens the superconducting energy gap in the perturbed S2 layer preventing its manifestation in the CVC of the injector.
The invention is directed to a device and method to engineer the superconducting transition width by suppressing the phonon populations responsible for the Cooper-pair decoherence below the superconducting transition temperature via phononic bandgap engineering. The device uses phononic crystals to engineer a phononic frequency gap that suppresses the decohering thermal phonon population just below the Cooper-frequency, and thus the normal conduction electron population. For example, such engineering can relax the cooling requirements for a variety of circuits yielding higher operational quality factors for superconducting electronics and interconnects.
We have fabricated and characterized double-barrier multi-terminal superconducting transistor-like devices with the Nb/Al/AlOx/Al/Nb/Ni/Al/AlOx/Al/Nb (S1IS2FIS3) structure, where S, I, and F refer to superconducting, insulating, and ferromagnetic layers, respectively. A thin ferromagnetic Ni layer screens the superconductivity of the middle Nb layer on the injector-barrier side, so that the Nb/Ni bilayer manifests itself as a superconductor in the current-voltage characteristic (I-V curve) of the acceptor S1IS2junction, but as a normal metal in the I-V curve of the injector S2FIS3junction. It is shown that this property allows for considerable improvement of the input-output isolation of the quasiparticle-injection devices as compared with that for the formerly reported quiteron.
An underground communicating device has a low-noise SQUID using high temperature superconductor components connected to detect a modulated external magnetic flux for outputting a voltage signal spectrum that is related to the varying magnetic flux. A narrow bandwidth filter may be used to select a portion of the voltage signal spectrum that is relatively free of power line noise to output a relatively low noise output signal when operating in a portion of the electromagnetic spectra where such power line noise exists. A demodulator outputs a communication signal, which may be an FM signal, indicative of a modulation on the modulated external magnetic flux.
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.