SIZE EFFECT OF INNER RADIUS ON CIRCULARLY SYMMETRIC SOLITON STATES IN ANNULAR JOSEPHSON JUNCTIONS

The effect of the inner radius of an annular Josephson junetion on the excitation of circularly symmetric soliton states is explored by direct numerical simulation. In a circularly symmetric annular Josephson junction (CSAJJ hereafter), the phase difference in the order parameters \Phi across the junction bar-rier obeys the modified sine-Gordon equation (SGE) in which there is a perturbation term \Phi_p/\rho inversely proportional to the radial coordinate \rho. and this term does not appear in the case of a 1D in-line junc-tion. The effect of the \Phi_p/\rho term becomes prominent when \rho is small. It turns out that for junctions of grven dissipation and annular width, there is a lower limit of the inner radii for the junctions to support stable soliton motion, while the lower limit depends strongly on the dissipation coefficient \alpha. For example, for a CSAJJ with inner radius 5\lambda_J, outer radius 10\lambda_J, no stable soliton states would exist when \alpha=0.01 or \alpha=0.02. However, for 0.06≥\alpha≥0.03, there are ring-shaped solitary wave solutions, presumably because the dissipation suppresses the effect of the \Phi_p/\rho term. Finally, the behaviour of the seliton states and the rele-vant I-V characteristics are also disscussed.