Fluxoid quantization effects in high-T_c superconducting double networks

We describe a study of fluxoid quantization effects in a novel superconducting network consisting of two interlaced sub-networks of small and large loops. Computer simulations show different behavior for the sub-networks in this double network. In particular, while the occupation of the large loops by fluxoids grows linearly with the external magnetic field, the small loops occupation grows in steps, similar to the occupation of a single loop. Magnetoresistance measurements in a double network made of MBE grown La _1.84Sr0.16CuO₄ reveal periodic oscillations resembling that of a single loop with field periodicity as found in the Little-Parks effect. However, the amplitude of the oscillations is found to be larger by almost two orders of magnitude than that expected from this effect. We propose a new model attributing these oscillations to the interaction between moving vortices and the periodic persistent current induced in the loops by the external field. This model explains the large magnetoresistance amplitude as well as its temperature dependence.