Vortex configurations and geometrical shapes of superconducting MoGe networks revealed by scanning SQUID microscope*

We prepared square networks of MoGe films by a standard photolithographic technique to observe vortex penetration into the network by means of a scanning SQUID microscope under different conditions of applied magnetic fields and temperatures. We found that vortex distribution in network evolves with applied magnetic field. At half matching field, vortices showed a checkerboard pattern, being in good agreement with theoretical predictions. We also investigated how vortices occupy network holes at different temperatures. Vortices tend to align in a ``diagonal'' direction at high temperatures while vortices repel each other to become isolated vortices at lower temperatures. Our results are consistent with theoretical calculation for nanoscopic superconducting network using the nonlinear Ginzburg-Landau equation. We also demonstrate that our data processing method appreciably improved a spatial resolution of the SQUID microscope.