Anomalous matching effect in the magnetization of the triangular microhole lattice on a Pb film of 7.5 μm lattice constant

We have investigated the magnetization of a triangular microhole lattice on a Pb film by means of a SQUID magnetometer under small dc fields (| H | ≤ 4.7 Oe). We find sharp magnetization peaks at the integral multiples of the magnetic matching field at a temperature near the critical temperature T c . Anomalously, the matching peaks are symmetric and reversible against the field reversal. Therefore, neither the Little–Parks effect nor the preferential pinning effect at the matching fields can explain this phenomenon. The half-integer subharmonic peaks are also observed while they are very weak. We have also carried out magnetization measurements under high dc fields (| H | ≤ 1000 Oe) to investigate a phase diagram covering the superconducting regime completely. We find the irreversibility line in the superconducting state.