Evaluation of supercurrent distribution in High-TC superconductor by Scanning SQUID Microscopy

Scanning SQUID Microscope (SSM) is a powerful tool for observing small magnetic flux. It measures the z-component signal of flux density, but it is also available for observation of current distribution by inverting the Biot-Savart law. We report the two dimensional (2D) vector mapping of current distributions in high-TC superconducting YBa2Cu3O7−y (YBCO) thin films obtained by converting magnetic-field data measured by SSM. The current distribution contains those from both transport supercurrent and vortex current. The transport supercurrent is found to flow mainly along the edge of a stripline. The results are in good qualitative agreement with the calculated results based on simple London model. The YBCO films with an artificial grain boundary, i.e. Josephson boundary are also observed. The transport current seems to flows with avoiding the vortices, and an irregular vortex is observed at a point of grain boundary

Images of interlayer vortices and c-axis penetration depth of high-Tc YBa2Cu3O7–y superconductor

The measurements on the magnetic image of interlayer vortices are performed for the high- Tc YBa2 Cu3 O7-y (110) thin film using a high sensitive scanning SQUID microscopy. Clear images of aligned giant interlayer vortices are observable. For the majority of vortices, using the London model, the c -axis penetration depth is estimated to be about 20 μm at 3 K. The temperature dependence of λc is obtained from the observed vortex images at different temperatures, whose behavior is in good agreement with those of the microwave cavity measurement

Temperature Dependence of Half Flux Quantum in YBa2Cu3O7−y Tricrystal Thin Film Observed by Scanning SQUID Microscopy

One of the most important topics in high critical temperature superconductors is the symmetry of order parameter. The most powerful and direct method to show the evidence of d-wave symmetry is the measurement of the half flux quantum at the tricrystal boundary of a superconducting thin film. We present the observation of the half flux quantum in a YBa2Cu3O7−y thin film on a SrTiO3 tricrystal substrate by using a scanning SQUID microscope (SSM). The SSM observation is done from 3 to 90 K. The vortex at the tricrystal point corresponds to Φ0∫2(=1.03×10^-15Wb) and this half vortex is observable up to near the critical temperature. The results indicate the evidence of dx2−y2 symmetry of the superconducting order parameter. Josephson vortices at grain boundaries are also observable and some of them are mobile with increasing the temperature.This work has been supported by Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Corporation (JST)

Supercurrent distribution in high-TC superconducting YBa2Cu3O7-y thin films by scanning superconducting quantum interference device microscopy

The two-dimensional vector mapping of current distributions in high-TC superconducting YBa2Cu3O7-y thin films obtained by converting magnetic-field data measured by scanning superconducting quantum interference device (SQUID) microscopy is reported. The current distribution contains the contributions from both transport supercurrent and vortex current. The transport supercurrent is found to flow mainly along the edge of a stripline, and the numerical calculation based on the simple London model by taking the specific sample-detector geometry into account is given. The agreement between the experimental data and the calculated results is good, demonstrating that the scanning SQUID microscope provides a useful tool for studying the current distribution in a superconductor