Model for the fine structure of zero field steps in long Josephson tunnel junctions and its comparison with experiment

Abstract

The single fluxon dynamics in the resonant regime has been investigated on high-quality low-loss Nb/Al–AlOx/Nb window Josephson tunnel junctions. A new model accounting for the fine structure of zero field steps in linear junctions is proposed. Depending on the fluxon velocity and on the junction losses, resonances may occur between the fluxon and the plasma waves corresponding to different wave numbers. This mechanism relies on a single proposition that the fluxon experiences an acceleration approaching the nonideal boundaries of the junction. We find good agreement between theory, numerical simulations, and experiments. The presence of the idle region has been proved to play a determinant role for the occurrence of the fine structure.

Influence of the passive region on zero field steps for window Josephson junctions

“…These show up as steps in the zero field steps (ZFS) in the IV characteristics. The experiments conducted in this geometry, for a fixed set of electric parameters [8] confirm these findings.…”

“…For example Thyssen et al in [14] show a slight shift in the position (and therefore limiting fluxon velocity) of the IV curves for different values of w ′ . Ustinov et al [8] also display IV curves which depend on w ′ and large substructures. Recent numerical work [7] on a Josephson window junction with a lateral passive region and periodic boundary conditions along the propagation direction confirm these resonances due to Cerenkov radiation between a soliton travelling faster than v = 1 and the radiation of phase speed v φ = 1 + 1/k 2 > 1.…”

Linewidth of submillimeter wave flux-flow oscillators

“…A fine structure superimposed on the flux-flow steps was found; this structure results in a complicated dependence of the FFO linewidth on the magnetic field and bias current. Similar fine structure has been found previously [11][12][13][14] in connection with Fiske steps and zero field steps in the IV-curve of long Josephson junctions. The structure was ascribed to the resonance between the fluxons and excited plasma waves.…”

Fluxon dynamics in long annular Josephson tunnel junctions

“…The fine structures have often been reported since 1981 on the zero-field singularities of a long linear junction [16][17][18] and several models have been proposed to explain them. Chang et al 16 related the fine structures to the interaction of p fluxon oscillations with the qth fractional cavity mode, assuming the response of the Josephson resonator to be linear.…”

“…In this case, the resonant frequencies should occur at f n ϭf p /n. 17 In a recent paper Barbara et al 18 described the development of the fine structures at low temperatures as due to the interaction between the fluxon and the plasma waves generated by the fluxon itself during the acceleration experienced at reflection on the junction edges. Unfortunately none of the previous explanations seem to be able to fit the voltage position of the fine structures we observed.…”