Time-Resolved Photoresponse in the Resistive Flux-Flow State in Y-Ba-Cu-O Superconducting Microbridges

186 LLE Review, Volume 95 Introduction High-temperature superconductors (HTS’s) exhibit many properties that are very desirable for microwave-based telecommunication applications. Their main advantages are low absorption at microwave frequencies1 and existence of HTS microwave devices based on the controlled vortex flux flow.2 The mostpromising material is the YBa2Cu3O7–x (YBCO) superconductor because of its well-developed technology for the fabrication and patterning of very high quality epitaxial thin films, as well as the ability to produce multilayer microstructures. YBCO is characterized by a very large critical current density Jc > 2 to 3 MA/cm 2 at nitrogen temperatures3 and exhibits ultrafast (~1-ps) voltage photoresponse when optically excited with femtosecond laser pulses.4 Thus, YBCO thin films and microstructures are good candidates for generating high-power and jitter-free ultrafast electrical transients for ultrawide-frequency-band antennas5 for mobile communication systems. The ultrawide-band signals can be reflected by any conductor or insulator with dimensions fitting the wavelength of the signal. Therefore, the GHz-bandwidth, jitter-free pulse-driven antennas are desirable devices for high-resolution pulsed-radar systems, operating with a high (GHz) repetition rate of probing signals.