Fluxon modes and phase-locking at 600 GHz in superconducting tunnel junction nonuniform arrays

Abstract

We investigated parallel arrays of superconducting Nb/ AlO x / Nb tunnel junctions nonevenly distributed in a superconducting Nb/SiO/Nb microstrip transmission line. Such devices are discretized Josephson transmission lines ͑DJTLs͒ in which, from theory, magnetic flux quanta ͑"fluxons"͒ can travel as solitonic waves when a dc current bias and a dc magnetic field are applied. We observed a reproducible series of resonant branches in each device's I − V curve, at Josephson submillimeter-wave frequencies ͑from 240 to 720 GHz͒ matching the resonances predicted using a transmission line analysis, where the loading of the N = 5 junctions is fully taken into account. The nonperiodic distribution was optimized to provide rf matching over a large bandwidth ͑450-650 GHz typically͒, implying that the plasma resonance of junctions is inductively tuned out over a similar band by the array. A confirmation of this comes from the observation, at frequencies higher than the untuned junctions plasma frequency, of several Josephson phenomena reported in this article: Fiske-like resonances, phase-locking of the n = 3 resonance to an external 600 GHz microwave source, rf-induced zero crossing, and resonances at fractional harmonics of the rf signal. These experimental results are all compatible with a fluxon-based resonances interpretation, as in the extensively studied long Josephson junctions yet at higher frequencies. As reported elsewhere, we could detect ϳ500 GHz microwave radiation emitted by our devices in the n = 1 and n =3 modes. In light of these unique properties, we propose nonuniform DJTLs as a promising type of Josephson device for submillimeter-wave oscillators and fast fluxon-based electronics.

Chaotic movement of vortices in superconductors of high-Tc superconducting maglev system at a high speed

“…It is noticeable that Eq. (5) is mathematically equivalent with a model of the Josephson junction array [22], which has been intensively investigated from contexts of the resonance and synchronization including chaotic behaviors [23][24][25], although the present periodically pinned vortices and Josephson junction array are two different physical systems. The mathematical equivalency of the two systems provides a useful connection to reveal their universal features, thus, deepening the understandings of the intrinsic mechanism behind the different physical phenomena.…”