Interstitial flux phases in a superconducting niobium film with a square lattice of artificial pinning centers

We demonstrate that a square lattice of artificial pinning centers in a superconducting Nb film induces the formation of highly ordered interstitial vortex phases with different symmetries for external magnetic fields as high as the eighth matching field. These {open_quotes}supermatching{close_quotes} phases are identified by distinct differences in the behavior of their critical currents, magnetoresistivity, and magnetization. Our results are consistent with predictions of supermatching lattice symmetries by recent numerical simulations. {copyright} {ital 1999} {ital The American Physical Society}