Novel Pinning Phenomena in Nb Thin Films with the Heterostructure Pinning Arrays

Superconductor thin films with full or partial regular triangular hole arrays have been fabricated to explore the vortex pinning behavior. Electron beam lithography and reaction dry etching techniques have been used. The area of the regular square hole arrays is changed from 50umx50um for sample A to 50umx5um for samples B and C, and the area of the superconducting film remains the same. Magnetotransport measurements were carried out by a four-probe technique. Periodic critical current matching peaks are observed for all three samples. The small area hole arrays and their neighboring normal superconducting film without holes form heterostructure and novel pinning phenomena are observed. At certain temperatures, sample A has five matching peaks. However, samples B and C have two and one matching peaks, respectively. A strange phenomenon is observed that a negative resistance appears for the heterostructure films at zero field.