Role of the pinning effect on quantum phase transition in superconducting Ta thin films with the addition of artificial periodic pinning centers

In order to study the influence of vortex pinning effect on the superconductor-insulator transition, we introduced periodic hole arrays as strong pinning centers into superconducting tantalum thin films which are representative weakly disordered films where metallic behavior was reported. The low temperature transport characteristics of the perforated tantalum thin films with various areal number hole densities were investigated under perpendicular magnetic fields. The increase of strong pinning centers leads that the strongly trapped flux density increases, and thus causes that the superconducting state expands and the metallic behavior is suppressed. In addition, we found that flux distance between weakly pinned interstitial vortex and its adjacent vortex is constant regardless of areal number hole density. One of possible interpretations for understanding this observation is that the constant flux distance for the appearance of metallic behavior is related to vortex localization length of quantum tunneling of vortices.