Investigation of ErBa2Cu3O7/Cu2 O/normal metal tunnel structures

Tunneling studies have been made using sputtered Cu₂O as an insulating barrier between an EBCO thin film and a normal metallic layer. Cu₂O was selected for its low potential for chemical reaction with the superconducting layer and for its photoconductive properties. Having a band gap in the visible (2 eV), Cu₂O is a suitable candidate for photosensitive tunneling experiments. EBCO thin films were deposited in situ onto MgO substrates using an off-axis sputtering technique. T_c´s of as-deposited films were between 80 and 85 K. Inductively measured J_c´s ranged between 10⁶ and 10⁷ A/cm² at 4 K. A 5-20-nm layer of Cu₂O was sputtered directly on top of the superconducting film. Room-temperature resistivities of the Cu₂ O layer were typically greater than 10⁶ Ω-cm. A normal metal layer (typically gold) was then deposited onto the Cu₂ O layer. Transport properties of the structure were measured at temperatures ranging above and below the T_c of the superconducting layer. Measurements of structures fabricated to date showed no tunneling effects. Measurements of the I-V characteristic of a Cu/EBCO bilayer exhibited nonohmic behavior at 85 K and 4 K, indicating the existence of an extraneous interfacial layer. Preliminary results on one such structure indicate possible tunneling effects