Rapid optical switching of latched electrical resistance in a high- T c superconducting tape

We report microsecond timescale switching between the superconducting and normal states of commercially manufactured high-Tc superconducting wires using optical radiation to heat the conductor above Tc. The achieved voltages and switching times have significant implications for a new class of thermal switches. The report contains experimental data for photo-induced microsecond scale voltage transients as well as numerical analysis of heat propagation through the material in response to optical radiation. The microbridges are etched into commercially manufactured coated conductors and submerged in liquid nitrogen. By varying the magnitude of the transport current, two different optical responses are identified. At low transport currents, short-lived voltage transients occur, transitioning to persistent latching once the current is increased above a threshold value. The microbridge, therefore, behaves as a fast opening and closing switch when carrying low currents or an optically latched thyristor at high currents. This is understood to occur due to critical current suppression as a result of heating from the optical pulse. Optically induced heating reduces the superconducting volume fraction, and Joule heating due to the transport current interaction with the high temperature superconducting occurs, which either causes short-lived or stable self-heating normal regions dependent on the magnitude of the transport current. This study is concluded with an estimate of the energy necessary to drive the microbridge into the resistive state. The observed behavior can potentially be utilized as a switching element in superconducting transformer rectifiers where high frequency switch operation is required.