Evidence for Current-Driven Phase Slip Lines in Submicron High-$T_c$ Superconducting Wires

We present superconducting current-voltage characteristics of submicron YBa$_2$Cu$_3$O$_{7-\delta}$ wires. The submicron-wide wires were fabricated using a chemical-free technique based on selective epitaxial growth. Pulsed current-biased and voltage-biased measurements were made between 4.2 K and $T_c$ and as a function of an applied magnetic field. The current-voltage characteristics exhibit distinctive behaviour suggesting that the current-driven or voltage-driven transition of our submicron high-$T_c$ wires into the resistive state is through the formation of phase slip lines.