Dynamical I-V Characteristics of SNS Junctions

We probe the dynamics of a Superconductor /Normal Metal/ Superconductor junction (SNS: Nb / Al above its critical temperature / Nb) by measuring~ its voltage / current characteristics while applying an ac current of frequency in the range 1-200 MHz. We observe a dynamical phase transition as a function of the frequency and amplitude of the ac current. At low frequency there is a continuous change in the dynamical behavior of the junction, replaced an abrupt change and hysteresis at high frequency. The crossover frequency between the two regimes has a strong temperature dependence similar to that of the electron-phonon interaction rate.