Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions

Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV=2/spl Delta/ as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d(x/sup 2/-y/sup 2/) (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with T/sub c/=62 K, the Josephson current is measured as a function of junction resistance, R/sub n/, which varied by two orders of magnitude (1 k/spl Omega/ to 100 k/spl Omega/). I/sub c/R/sub n/ product is proportional to the 0.47 power of I/sub c/ and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (T/sub c/=62 K) to the underdoped regime (T/sub c/=70 K), the average I/sub c/R/sub n/ product increases as does the quasiparticle gap. The maximum I/sub c/R/sub n/ is /spl sim/40% of the /spl Delta//e at each doping level, with a value as high as 25 mV in underdoped Bi-2212.