Growth and characterization of high-T-c based heterostructures

We have investigated several trilayers based on the Bi2 Sr2 CaCu2O8+δ and YBa2Cu3O7-δ families. Our trilayers were realized using Bi2Sr2YCu2O8+δ and PrBa2Cu3O7-δ oxide barriers respectively with thicknesses ranging between 100 Å and 300 Å. The films have been grown on (001) SrTiO3 substrates by means of dc sputtering deposition in high pressure oxygen plasma. Electrical resistivity measurements showed Tc= 87 K and 91 K for the Bi2Sr2CaCu2O8+δ and YBa2Cu3O7-δ electrodes, respectively, and a semiconductor-like behavior of the Bi2Sr2YCu2O8+δ and PrBa2Cu3O7-δ nonconducting layers. In the case of Bi2Sr2CaCu2O8+δ/Bi2Sr2YCu2O8+δ/Bi2Sr2CaCu2O8+δ junctions, the tunneling dynamical conductance, G(V), at low temperatures, indicated gap-like structures at ±30mV. For the YBa2Cu3O7-δ/PrBa2Cu2O7-δ/YBa2Cu3O7-δ junctions, the G(V) showed gap features with very well defined maxima at ±45mV and a very low conductance at zero bias. We discuss both these behaviors in close comparison with the results obtained in high-Tc based tunnel structures with natural barriers.