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

摘要

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 fine 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.