Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions

摘要

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+(delta)) (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV =2A as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d(sub 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(Omega) to 100 k(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 thehole 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 (approximately) 40% of the (Delta) /e at each doping level,with a value as high as 25 mV in underdoped Bi-2212.