Intrinsic Josephson tunnelling properties in small-sized Bi-Pb-Sr-Ca-Cu-Cu-O mesas

In order to understand the intrinsic Josephson tunnelling properties, the current-voltage (I-V) characteristics of small-sized intrinsic Josephson junctions in (Bi1-xPbx)(2)Sr2CaCu2Oy (B(P)SCCO) single crystals with x = 0, 0. 15 and 0.2 are investigated. By reducing the mesa size, reproducible I-V characteristics of intrinsic Josephson junctions were successfully measured. All fabricated mesas exhibit typical multiple branching in their I-V curves, which are independent of x. In addition, a well-defined gap structure without negative resistance is observed for the mesas that have dimensions less than a few mum(2). The gap parameter Delta of these materials is similar to 25 meV at 4.2 K. The critical current density J(c) at 4.2 K depends on x. The quasiparticle characteristics and the temperature dependence of critical currents are discussed by the d-wave tunnelling model.