Narrow Results

We investigate critical current (I_c) modulation of stacked Josephson junctions (SJJs) dc superconducting quantum interference device (dc SQUID) on a Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) whisker. A coupled SJJs with a completely perforated hole of 0.1 μm × 0.2 μm were fabricated by using a 3-D focused-ion-beam (FIB) etching method. Those dc SQUIDs exhibited uniform multi-branch structures and clearly oscillated critical current under external magnetic fields (H_e). With applying H_e, the clear periodic modulation patterns of I_c are obtained and well fitted to the calculated value from the loop area of 0.02 μm².

When a magnetic field is applied parallel to the superconducting layers in high-T_c superconductors (HTSCs), vortices become Josphson vortices (JVs). To study the magnetic phase diagram of JVs in strongly anisotropic HTSCs, we propose that the JV flow-resistance measurement is a powerful probe to observe periodic oscillations in the JV flow-resistance against the magnetic field. We could determine the magnetic phase diagram of JVs in Bi-2212, in which there exist a three-dimensionally-ordered state and a two-dimensionally quasi-ordered one.