Pinning effects induced by periodic arrays of structural corrugations in Nb thin films

Abstract

Artificial vortex pinning arrays have been fabricated by electron-beam lithography in conjunction with reactive ion etching in Nb superconducting thin films in order to investigate flux pinning. Based on the structural corrugation in the Nb thin film, the square lattice of defects that act as pinning centers was created. A strong periodic pinning effect, as the vortex lattice matches the array of defects, can be observed in the evolution of resistivity and critical current with the applied magnetic fields in the mixed state of the Nb film, thus, revealing a synchronized pinning effect due to structural corrugation. This result is in agreement with the resistivity-temperature curves at matching fields and half-integer matching fields in which a crossover occurs for temperatures exceeding a certain threshold value. The phenomenon is related to the presence of the pinning structure at matching fields.