Abstract
The Scannign SQUID Microscope (SSM) system has been widely used in flux distribution image, pairing symmetry verification, defects distribution,...etc. One of the important issues in constructing the SSM system is to design and fabricate a practical dc SQUID which has high SNR during operation. Fortunately, with the collaboration to Superconducting Device Lab which was led by the associate research fellow of Academia Sinica Institute of Astronomy & Astrophysics (ASIAA), Dr. Wang, Ming-Jye, by using our own Nb-AlOx-Nb technology, we have successfully developed a SSM system. In this paper, I will discuss about the characteristics of our home-made dc SQUID and the performance of our SSM system briefly.We have deposited some Nb thin film with different geometry, and imaged the magnetic field distribution by SSM system. The current discontinuity consideration is consistence to our magnetic field distribution images. The SSM system also helps us in observing the vortices penetration behavior, the edge vortices pinning and the distribution of vortex and anti-vortex. In this paper, I will show you some observations about the flux images of the practical Nb thin film. I will introduce two different theories in discussing the vortex penetration of type II superconductor, the Bean-Livingston model and the calculations from Zeldov et al. However, our observations about the vortex penetration behavior of practical type II superconducting thin film were not consistent with these theories fully. We also observed some interesting results about the vortex pinning related to the anti-vortex penetration distribution.