rf impedance of superconducting weak links

Expressions of the rf impedance of superconducting weak links are obtained by the use of derived solutions of the nonlinear equation describing a resistive shunt junction model of superconducting weak links. It is shown that the real part of impedance is always positive in the zeroth current step region and it can be negative in the first current step region for low power of incident rf radiation. The calculated values of the rf impedance in the zeroth and the first current step regions from the derived expressions of the rf impedance is in good agreement with the calculated ones by Auracher and Van Duzer. The condition for amplification of incident rf radiation is derived. (auth.)