Growth and characterization of high-Tc based heterostructures

They have investigated several trilayers based on the Bi2 Sr2 Ca Cu2 O8+δ and YBa2 Cu3 O7-δ families. Their trilayers were realized using Bi2 Sr2 Y Cu2 O8+δ and Pr Ba2 Cu3 O7-δ oxide barriers respectively with thicknesses ranging between 100 A and 300 A. The films have been grown on (001) Sr Ti O3 substrates by means of dc sputtering deposition in high pressure oxygen plasma. Electrical resistivity measurements showed Tc = 87 K and 91 K for the Bi2 Sr2 Ca Cu2 O8+δ and YBa2 Cu3 O7-δ electrodes, respectively, and a semiconductor-like behavior of the Bi2 Sr2 Y Cu2 O8+δ and Pr Ba2 Cu3 O7-δ nonconducting layers. In the case of Bi2 Sr2 Ca Cu2 O8+δ / Bi2 Sr2 Y Cu2 O8+δ / Bi2 Sr2 Ca Cu2 O8+δ junctions, the tunneling dynamical conductance, G (V) at low temperatures, indicated gap-like structures at ± 30 mV. For the YBa2 Cu3 O7-δ / Pr Ba2 Cu3 O7-δ / YBa2 Cu3 O7-δ junctions, the G(V) showed gap features with very well defined maxima at ± 45 mV and very low conductance at zero bias. They discuss both these behaviors in close comparison with the results obtained in high-Tc based tunnel structures with natural barriers