Vortex Penetrations in Parallel-connected two Stacks of Intrinsic Josephson Junctions

In mesoscopic stacks of intrinsic Josephson junctions (IJJs) in Bi2Sr2CaCu2O8+y (Bi2212), the penetrations of individual vortices are detectable by the measurements of the transport properties, i.e., c-axis resistance or critical current. We have measured the c-axis resistance as a function of magnetic field in samples with two stacks of IJJs connected in parallel by Bi2212 itself to study any interaction of individual vortex penetrations into them. Since the superconducting loop containing two stacks of IJJs is the same geometry as that of superconducting quantum interference device (SQUID), we might expect a periodic resistance (or current) modulation as a function of magnetic field, whose period corresponds to the area in the loop. However, the results were just simple mixing of the resistive changes by the individual vortex penetrations into each of the stacks; behavior like SQUID has not been observed in present samples.