Flux jump in superconducting Pb networks at fractional numbers of the matching fields

The extended Little-Parks effect of superconducting network is known as a periodic Tc variation as a function of magnetic field. Superconducting Pb honeycomb networks of matching field 0.106 G and triangular microhole lattice of Pb of matching field 0.425 G have been fabricated by the combined techniques of the electron beam lithography and a lift-off process of evaporated Pb films. The application of magnetic field corresponds to the vortex doping into networks. We measured the magnetization of the networks systematically by using a SQUID magnetometer. We found that flux jump appears rather periodically as a function of magnetic field. Flux jumps may be induced by a periodic decrease in the critical current density of the network. To the authors' knowledge, this is for the first time to observe the extended Little-Parks effect appeared in flux jumps. We also discuss the anomalous matching effect.