Tunneling studies in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/

Planar tunnel junctions have been realized on liquid-etched Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO) single crystals with natural barriers and Pb, Pb-Bi, Au counterelectrodes. At T=4.2 K and I-V characteristics of these junctions often show multiple switches that disappear at the T/sub c/ of the BSCCO compound. The dV/dI vs. V curves show gaplike structures at about +or-22 mV and second features at about +or-40 mV. These are very similar to the double structure observed in YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) junctions. The background resistance above the gaplike features is flat in the majority of the junctions, while about 20% of the junctions show decreasing resistance with bias. For Pb and PbBi counterelectrodes, negligible leakage currents at low temperatures indicate good quality tunnel barriers, continuous and pin-hole free. The phonon structures of these materials indicate a single-step tunneling process. The behavior of the zero-bias resistance dip observed in some junctions is discussed.<>