Flux pinning force in Nb thin films with periodic vortex pinning arrays

Abstract

Flux pinning force has been investigated in superconducting Nb thin films with square arrays of artificial flux pinning centers. These pinning centers due to the structural corrugation in the Nb thin film were created. In the mixed state, the magnetoresistance minima and critical current density maxima to be separated at constant field intervals corresponding to the matching fields were found. The temperature dependence of critical current density can be fitted to an expression (1−T/TC0)n near superconducting transition temperature. The n values at applied field equal matching fields (H=H1,H2,H3…) are 5/2, in contrast to 3/2 at half integer matching fields. It indicates that the dynamics of interstitial vortices at higher matching fields is similar to those at the first matching field. It can be believed that the collective flux pinning force stabilized by the vortices on pinning centers indirectly prevents interstitial vortices from flowing.