Vortex imaging in Tl-based superconductors with a scanning SQUID microscopy

Vortex images of superconducting material Tl-1223 thin film taken with a scanning SQUID microscope are presented. Among the vortices images, coexistence of vortex-antivortex pairs is observed at low field region. Short distances of the pairs indicate the existence of strong pinning centers in this material.