Investigation of high-temperature superconductors with terahertz bandwidth electrical pulses

The authors summarize recent attempts to propagate ultrashort electrical pulses containing frequency components up to 1 THz on transmission lines made from thin films of the high-temperature superconductor YBa₂Cu₃O_7-δ. Optoelectronic generation of extremely short electrical transients and jitter-free electrooptic detection of the pulse shape and amplitude as they propagate along the superconducting line make it possible to investigate the high-frequency properties of the high-T_c material with high accuracy because of the the long interaction lengths that are possible on transmission lines. The authors discuss the influence of epitaxy, surface roughness, and magnetic field on the pulse propagation. Important parameters such as the magnetic penetration depth and the superconducting energy gap are directly determined from the experimental data. Finally, the authors compare their results with weak-coupling BCS (Bardeen-Cooper-Schrieffer) theory