Tunneling Study of Optimal Doped and Overdoped BSCCO 2212

Using a point contact method, both SIN and SIS junctions have been made on single crystals of overdoped BSCCO 2212 with Tc values near 62 K. The dynamic conductances of the SIN junctions (Au tip) are qualitatively similar to those found on optimally doped BSCCO 2212 but with reduced gap values. Typically, Δ= 15 meV to 20 meV for the overdoped crystals reduced from the maximum value of 30 meV for optimal doped BSCCO. Reproducible SIS junctions are obtained between two pieces of the BSCCO crystal which display well-resolved quasiparticle and Josephson currents. The maximum Josephson current depends on junction resistance and is consistent with Ambegaokar-Baratoff theory. The high bias conductance data display the asymmetric dip feature as is found in optimal-doped BSCCO but we have found that dip is just part of a larger spectral feature that extends out to 400 mV.