Discreteness-induced resonances and ac voltage amplitudes in long one-dimensional Josephson junction arrays

Abstract

New resonance steps are found in the experimental current-voltage characteristics of long, discrete, one-dimensional Josephson junction arrays with open boundaries and in an external magnetic field. The junctions are underdamped, connected in parallel, and DC biased. Numerical simulations based on the discrete sine-Gordon model are carried out, and show that the solutions on the steps are periodic trains of fluxons, phase-locked by a finite amplitude radiation. Power spectra of the voltages consist of a small number of harmonic peaks, which may be exploited for possible oscillator applications. The steps form a family that can be numbered by the harmonic content of the radiation, the first member corresponding to the Eck step. Discreteness of the arrays is shown to be essential for appearance of the higher order steps. We use a multi-mode extension of the harmonic balance analysis, and estimate the resonance frequencies, the AC voltage amplitudes, and the theoretical limit on the output power on the first two steps. 85.25.Am,85.25.Cp,74.50 Typeset using REVT E X 1

Amplification of electromagnetic waves excited by a chain of propagating magnetic vortices in YBa2Cu3O7−δJosephson-junction arrays at 77 K and above

“…Further increases of the current do not lead to further linear increases in the vortices velocity, because the energy is consumed in amplifying the linear waves. Such resonances have been observed by many groups, below 9K, in JJ arrays made of low temperature superconductors (LTS) [4][5][6][7]. The associated amplified EM radiation has been measured too, proving that LTS JJ arrays are suitable candidates as B-tunable microwave oscillators [8,9].…”

“…A vortex corresponds to a kink (soliton) propagating along the chain. In this configuration, a given pendulum hangs almost straight down for much of the time, but [5]. To minimize this effect we designed our JJ array as a very long (N=440) and asymmetric array consisting of 22 identical sets of 20 junctions (pendulums) each (see Fig.…”

“…The inset ofFig. 3ashows the derivatives dI/dV of 7 consecutive IVC's(5)(6)(7)(8)(9)(10)(11)(12) just before, during, and after a (3, 4) mode crossing. Both m=3 and m=4 resonances, seen as peaks in the dI/dV versus V characteristics, are clearly visible just before and after the mode-crossing.…”

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

“…Solitons-corresponding to localized magnetic flux quanta, "fluxons"-are routinely observed at rest and in motion in LJJs. [26][27][28] Any type of DJTL is characterized by an effective Josephson length J ‫ء‬ Ͼ J , which may be greater or smaller than the cells length l cell , and tends to a LJJ as its continuous limit ͑l cell → ⌬x͒. 18,21,22 Unlike other submillimeter-terahertz sources which require frequency up-conversion or downconversion stages, Josephson oscillators built out of rugged, low-T c materials ͑e.g., Nb͒ radiate straightforward at these wavelengths ͑⌽ 0 −1 ·mVϳ 0.5 THz͒, 21,23,24 with a minute power consumption ͑in the W range͒.…”

Dual flux-to-voltage response of YBa2Cu3O7−δasymmetric parallel arrays of Josephson junctions

“…For the full text of this licence, please go to: http://creativecommons.org/licenses/by-nc-nd/2.5/ A parallel array of Josephson junctions (PAJJs) in an applied magnetic flux can either exhibit flux-flow [1][2][3][4][5] or behave like a sensitive flux-to-voltage interferometer (magnetometer) [6]. When damping is low flux flow dominates PAJJ's dynamics and they can be used as microwave generators [7][8] or superconducting transistors [9][10] [6].…”