Interlayer Transport of Quasiparticles and Cooper Pairs inBi2Sr2CaCu2O8+δSuperconductors

We study the $c$-axis transport of stacked, intrinsic junctions in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ single crystals, fabricated by the double-sided ion beam processing technique from single crystal whiskers. Measurements of the $I-V$ characteristics of these samples allow us to obtain the temperature and voltage dependence of the quasiparticle $c$-axis conductivity in the superconducting state, the Josephson critical current, and the superconducting gap. We show that the BCS $d$-wave model in the clean limit for resonant impurity scattering, with a significant contribution from coherent interlayer tunneling, describes satisfactorily the low temperature and low energy $c$-axis transport of both quasiparticles and Cooper pairs.