Dynamic behavior of superconducting microbridges

Measurements of the $I-V$ curves of superconducting thin-film tin microbridges are reported. A vortex flux-flow model is developed to explain, close to $T_c$, the regime where a plateau in current is observed. This regime is active when the coherence length $\xi$ is smaller that half the width $\frac{w}{2}$ of the bridge. At temperatures much closer to $T_c$, where $\xi \ge \frac{w}{2}$, the phase-slip mechanism is effective.