Explanation of the zero-bias anomaly in the tunneling characteristics of single-crystal Bi2Sr2CaCu2O8 with intrinsic Josephson tunneling

We present measurements of dV/dI and V vs I for Ag-single-crystal Bi2Sr2CaCu2O8-Ag NSN contacts. It was found that when the contact resistance was comparable to the sample resistance, zero-bias anomalies, as previously reported, were observed. We explain this observation by assuming that the sample contains intrinsic Josephson junctions between the CuO planes which become normal at higher current densities. We present a simple model based on this hypothesis which explains some aspects of the observed feature quantitatively. The effects of magnetic fields are also consistent with our observations. Recently, Josephson tunneling measurements have been used to determine the symmetry of the order parameter in YBa2Cu3O6.9. We believe that the presence of intrinsic Josephson junctions will make such experiments extremely difficult to interpret for Bi2Sr2CaCu2O8.