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

We have observed the supercurrent distribution in YBa2Cu3O7-delta (YBCO) st rip lines under bias current and magnetic fields using terahertz (THz) radi ation imaging. By mapping the amplitude of the THz pulses, which are emitte d from the YBCO strip lines excited by ultrashort optical pulses, the super current distribution is visualized. It is found that the spatial resolution of the obtained image depends on the excitation laser spot size. Irreversi bility of the current distribution between increasing and decreasing the bi as current is observed, which is semiquantitatively explained by the theore tical calculation based on the Bean critical state model for thin films. Th is technique can be a unique and powerful tool for the noncontact evaluatio n of the supercurrent distribution in high-T-c superconducting thin films. (C) 2001 Elsevier Science B.V. All rights reserved.