Abstract
To study the influence of sub-micron artificial pinning centers on vortex phases in high- T c superconductors, we have introduced holes array in Bi 2Sr 2CaCu 2O 8+ y single-crystal thin films using a focused ion beam. To preserve the quality of the crystals we made film samples from bulk crystals by the cleaving, and the surface of the Bi2212 films were covered by Au protection layer. The vortex-flow resistance shows a matching effect in the samples having triangular holes array which appears in vortex liquid phase of the pristine sample. This suggests that an in-plane symmetry is induced in the vortex liquid by regular holes array. Additionally, sub-harmonics of the matching effect are newly observed near the superconducting transition temperature ( T c). This suggests that the correlation length of pancake vortices is longer with approaching T c since the in-plane penetration depth diverges toward T c.
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