Supercurrent distribution in YBCO strip lines under bias current and magnetic fields observed by THz radiation imaging

Abstract

We have observed the supercurrent distribution in YBa 2Cu 3O 7− δ (YBCO) strip lines under bias current and magnetic fields using terahertz (THz) radiation imaging. By mapping the amplitude of the THz pulses, which are emitted from the YBCO strip lines excited by ultrashort optical pulses, the supercurrent distribution is visualized. It is found that the spatial resolution of the obtained image depends on the excitation laser spot size. Irreversibility of the current distribution between increasing and decreasing the bias current is observed, which is semiquantitatively explained by the theoretical calculation based on the Bean critical state model for thin films. This technique can be a unique and powerful tool for the noncontact evaluation of the supercurrent distribution in high- T c superconducting thin films.