Anisotropic flux penetration into Nb square superconducting networks

Abstract

Anisotropic flux penetration into square superconducting networks of Nb are studied by a magneto-optical imaging method. Their dependences on the lattice constant, the line width, the thickness of the networks, and temperature are systematically investigated. An anomalous diagonal flux penetration is observed (1) when the saturation number of vortices in a hole is equal to one possibly due to minimization of the Ginzburg–Landau free energy or (2) when the fan-shaped vortex penetration (vortex jet) from the corner of the square hole reaches the next-nearest-neighbor hole due to the enhanced current density with a high current–voltage exponent.