Origin of Diagonal Flux Penetration into Square Superconducting Networks

The origin of the anomalous diagonal flux penetration is investigated in Nb square superconducting networks. The magnetic field dependence and heat transfer coefficient dependence of this phenomenon are observed by using the magneto-optical imaging method. The anomalous diagonal flux penetration occurs independent of the applied magnetic field. Flux avalanches at low temperatures are suppressed by depositing a thick gold layer due to the enhancement of the thermal conductivity. However, the diagonal flux penetration appears even in the area covered by the gold layer. Combining these observations, we conclude that flux avalanches do not promote the diagonal flux penetration.