Observation of both pair and quasiparticle tunneling in intrinsic junction stacks fabricated on Bi2Sr2CaCu2O8+delta single crystals

We have investigated the tunneling properties of intrinsic Josephson junction stacks with various numbers N of CuO2 bilayers fabricated on underdoped Bi2Sr2CaCu2O8+delta Single crystals. The effect of gap suppression based primarily on nonequilibrium superconductivity can be significantly reduced with a reduction in N. For an N as few as 40, both pair and quasiparticle tunneling characteristics are clearly observed, It is shown that a clear gap 2 Delta of larger than 34 meV, the substantial conductance below the gap, and the I(c)R(N) product of less than 5 mV are the intrinsic features of tunneling along the c axis. Numerical calculation indicates that the quasiparticle current-voltage characteristics are consistent with the d-wave order parameter which is still suppressed by the nonequilibrium effect in a higher current region.