Abstract
In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper.
Highlights
The superconductor-insulator-superconductor (SIS) junctions carry two types of tunnel currents, namely the Cooper-pair tunnel current described by B.D
A low pass and bandpass filter was used at the input and output of the SIS junction respectively in order to ensure the proper propagation of the harmonic current and that only
The experimental results and modeling allow us to consider applications of the SIS junction as a comb-generator or a multiplier to attain useful level of power at second harmonic as demonstrated here and possibly at higher order harmonics e.g., 3rd or 4th harmonic. It was shown both through theory and experiment that the reactive of the quasiparticle tunnel current3–5 (QTC) of the SIS junction could be directly measured at specific bias voltages for the higher harmonics of the QTC
Summary
The superconductor-insulator-superconductor (SIS) junctions carry two types of tunnel currents, namely the Cooper-pair tunnel current described by B.D. Little work has been done in exploring higher order QTC harmonics in SIS junctions.[8,9] Recently, an experimental paper published by Billade et al.,[10] experimentally proved the presence of the second harmonic generated by an SIS tunnel junction series array consisting of 68 elements. The higher order QTC harmonics in an ideal SIS junction (where the quasiparticle nonlinearity is infinitely sharp) would be similar to the Fourier series of a Dirac delta function. We study the reactive part of the QTC and its impact on the QTC harmonic behavior. We demonstrate that direct measurement of the reactive QTC can be carried out at specific bias voltages for the higher harmonics of the QTC.
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