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arXiv:cond-mat/0405511 · Journal of Applied Physics

Josephson tunnel junction controlled by quasiparticle injection

Francesco Giazotto, Jukka P Pekola

Published Dec 23, 2004• 42 citations
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Abstract

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.

DOI
10.1063/1.1833576

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IEEE Transactions on Applied Superconductivity•Mar 1, 2001•2 citations
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.
We have fabricated and studied a stacked superconducting double tunnel junction device with transistor-like properties. The intermediate electrode is a bilayer consisting of a Nb film together with an Al film that acts as a quasiparticle trap. Large current gains of more than 50 are observed at 4.2 K when the Al layer is normal. The operation is highly directional. Results are explained on the basis of trapping of quasiparticles from a superconductor into a normal metal, together with a conversion of relaxation energy into electronic excitations. Similar devices should have wide applications in low-temperature measurement and detection systems.
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.
We propose a superconducting microwave relaxation oscillator based on a nanowire shunted by a resistor and an inductor controlled by quasiparticle injection from a tunnel junction positioned on it: the QUISTRON. This device exhibits relaxation oscillator behavior with DC voltage-controlled frequency tuning and DC current bias. The device frequency is modulated via the tunnel junction, which induces localized heating by injecting quasiparticles. This heating mechanism modulates the nanowire switching current, enabling relaxation oscillations when it falls below the bias current. We demonstrate the device operating principles and characterize its performance across various parameters, including different choices of shunt resistor, shunt inductance, and bath temperature ranging from 20 mK to 1 K. The device showed oscillation with a frequency range approximately between 1 GHz and 10 GHz and total energy dissipation per cycle of ∼100\sim100∼100 zJ. Our results suggest that this design offers a promising platform for compact, tunable superconducting oscillators in the microwave spectrum with potential applications in quantum information processing, microwave technology, and ultra-low-power electronics. The straightforward frequency control mechanism and integration potential make this device an attractive candidate for superconducting microwave local oscillators.
We propose a superconducting microwave relaxation oscillator based on a nanowire shunted by a resistor and an inductor controlled by quasiparticle injection from a tunnel junction positioned on it: the QUISTRON. This device exhibits relaxation oscillator behavior with dc voltage--controlled frequency tuning and dc bias. The device frequency is modulated via the tunnel junction, which induces localized heating by injecting quasiparticles. This heating mechanism modulates the nanowire switching current, enabling relaxation oscillations when it falls below the bias current. We simulate the device operating principles and its performance across various parameters, including different choices of shunt resistor, shunt inductance, and bath temperature ranging from 20 mK to 1 K. The device showed oscillation with a frequency range approximately between 1 and 10 GHz and total energy dissipation per cycle of approximately 100100100 zJ. Our results suggest that this design offers a promising platform for compact, tunable superconducting oscillators in the microwave spectrum with potential applications in quantum information processing, microwave technology, and ultralow-power electronics. The straightforward frequency control mechanism and integration potential make this device an attractive candidate for superconducting microwave local oscillators.
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.
A superconducting transistor with large current gain and bandwidth at low temperatures would have many applications. We have fabricated and tested a new three-terminal superconducting device with transistor-like properties at an operating temperature of 4.2 K. It is based on a stacked double tunnel junction structure where the intermediate film is a bilayer of superconducting Nb and an Al quasiparticle trap which can work 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, while large current gains of more than 50 are observed when the Al is in the normal state. The device shows a high degree of unidirectionality. The results can be explained on the basis of the recently proposed QUAsiparticle TRApping TRANsistor, which should have wide applications in detection systems operating at low temperatures.