I-V characteristics of a circularly symmetric annular Josephson junction.

Abstract

The I-V characteristics of a circularly symmetric annular Josephson junction are investigated numerically in this paper. By assuming a soliton solution in the junction initially, we found that in the absence of both an applied magnetic field and a feeding current there exists a quasisoliton solution for the equation ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{\ensuremath{\rho}}\mathrm{\ensuremath{\rho}}}$+${\mathrm{\ensuremath{\rho}}}^{\mathrm{\ensuremath{-}}1}$${\mathrm{\ensuremath{\varphi}}}_{\mathrm{\ensuremath{\rho}}}$-${\mathrm{\ensuremath{\varphi}}}_{\mathit{t}\mathit{t}}$-\ensuremath{\alpha}${\mathrm{\ensuremath{\varphi}}}_{\mathit{t}}$=sin\ensuremath{\varphi} so long as dissipative effects are excluded (i.e., \ensuremath{\alpha}=0). In the presence of the dissipative term (\ensuremath{\alpha}\ensuremath{\ne}0), such a quasisoliton solution does not exist. When a dc feeding current is introduced but the applied magnetic field is zero, the I-V characteristics show no evidence of zero-field steps. There does exist an Ohmic relationship in the I-V curve and a simple analytical treatment for this Ohmic behavior is made by assuming a rotary periodic solution for the equation. However, when a large external magnetic field is applied, the boundary conditions of this equation become asymmetric, which allows fluxon resonant propagation to occur within the junction. Hence we obtain a step-shaped I-V curve and these are considered to be Fiske steps. Finally, when the applied external magnetic field is small, we found no Fiske steps in the I-V curves.