Tunnelling anomalies in Bi2Sr2CaCu2O8-delta/Bi2Sr2YCu2O8-delta/Bi2Sr2CaCu2O8-delta planar junctions

We have prepared Bi2Sr2CaCu2O8−δ/Bi2Sr2YCu2O8−δ/Bi2Sr2CaCu2O8−δ (2 2 1 2 Y 2 1 2) planar heterojunctions (trilayer structures) using an in situ d.c.-sputtering process at high oxygen pressures onto (0 0 1) SrTiO3 substrates. Bi2Sr2YCu2O8−δ films (semiconducting-like) 10 and 12 nm thick were used as artificial barriers. Composition and structure of the barrier and the superconducting electrodes are entirely compatible which allows epitaxial growth of the entire heterostructure. Gap-like structures of about 30 mV have been determined from tunnelling characteristics of the junctions. Linear conductance backgrounds as well as Zero Bias Anomalies (ZBA) are reported and discussed in detail.