Time-domain observation of the development of phase-slip centers in superconducting filaments

We report the first observation of the time-domain development of phase-slip centers (PSC's). Using long one-dimensional indium microbridges that show PSC's on their dc $I-V$ curves, we apply fast-rising current steps in excess of their critical currents, and observe the development of the PSC's in time. We find a current- and temperature-dependent delay time for the development of each PSC, which we explain in terms of a simple theory.