Comparison of intrinsic Josephson and SIS tunneling spectroscopy of Bi2Sr2CaCu2O8+δ

Tunneling spectroscopy measurements are reported on optimally-doped and overdoped Bi₂Sr₂CaCu₂O_8+δ single crystals. A novel point contact method is used to obtain superconductor-insulator-normal metal (SIN) and SIS break junctions as well as intrinsic Josephson junctions (IJJ) from nanoscale crystals. Three junction types are obtained on the same crystal to compare the quasiparticle peaks and higher bias dip/hump structures which have also been found in other surface probes such as scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. However, our IJJ quasiparticle spectra consistently reveal very sharp conductance peaks and no higher bias dip structures. The IJJ conductance peak voltage divided by the number of junctions in the stack consistently leads to a significant underestimate of Δ when compared to the single junction values. The comparison of the three methods suggests that the markedly different characteristics of IJJ are a consequence of nonequilibrium effects and are not intrinsic quasiparticle features.