Periodic Peak Modulations in Bi-2212 Stacks Coupled to a Submicrometer Hole

Coupled stacked Josephson junctions (SJJs) in high-T_c superconducting (HTS) Bi₂Sr₂CaCu₂O_8+d (Bi-2212) are fabricated with a refined coupling configuration of a hole. Two types of coupled SJJs with a completely perforated hole of 0.1 mum x 0.2 mum and 0.2 mum x 0.4 mum were fabricated by using a 3-D focused ion beam (FIB) etching method. Those SJJs exhibited clearly oscillated critical current I_c 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 hole area of 0.02 mum² , DeltaB(= Phi₀/S) , where S is hole area. The width and uniform transport properties of SJJs are confirmed by flux flow resistance R_ff-H_e measurement with a bias current I_b of 1 muA at 10 K. We also investigated external field angle thetas_i dependence of junction resistance R_j at 1 T and 10 K. When a constant H_e of 1 T and a I_b of 1 muA are applied to the sample with changing thetas_i , unspecified equidistant and periodic peak structures in SJJs were induced. Those peaks dependence on thetas_i under H_e were experimentally observed by measurement of the R_j. We assign the origin of the peaks to the interrelations between the periodic mechanical vibrations of sample stage and the quantized flux behaviors around a submicrometer hole. Those peak structures of I_c and R_j could be excited by H_e,thetas_i,I_b, and some external signals from the peculiar properties of SJJs coupled to a hole.