Properties of Intrinsic Josephson Junctions in Bi_2Sr_2CaCu_2O_<8+δ> Single Crystals(Special Issue on Superconductive Electron Devices and Their Applications)

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We describe several properties of very thin stacks of 10 to 20 intrinsic Josephson junctions fabricated on the surface of Bi_2Sr_2CaCu_2O_<8+δ> single crystals. We show that the Joule heating is significantly reduced in these stacks and that the gap structure is clearly observable in the quasiparticle current-voltage (I-V) characteristics. The I-V curves are characterized by a large subgap conductance and a significant gap suppression due to the injection of quasiparticle current. It is found that the I_cR_n product of these intrinsic Hosephson junction stacks is significantly small compared with that expected from the BCS theory. It is also found that there is a tendency that I_cR_n decreases with increasing c-axis resistivity. Both I_c and the gap voltage exhibit unsaturated temperature dependence at low temperatures. The behavior presents a sharp contrast to that of Josephson junctions made of conventional superconductors. The characteristics are discussed in relation to the d-wave symmetry of the order parameter.
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1998-10-25