Bi₂Sr₂CuO_6+δ/ACuO₂ (A = Ca,Sr) superconducting multilayers obtained by molecular beam epitaxy

Bi-based superconducting multilayers, consisting of Bi₂Sr₂CuO_6+δ (2201) layers alternately stacked with CaCuO₂ or SrCuO₂ layers, have been deposited by Molecular Beam Epitaxy (MBE) using co-deposition and growth interruption techniques. In situ Reflection High Energy Electron Diffraction (RHEED) has been used to monitor the surface of the different layers giving evidence of a two-dimensional growth mode. The layered structure of the samples has been confirmed by X-ray diffraction analyses. Resistive measurements have shown superconducting 2201/CaCuO₂ samples with critical temperatures strongly depending on the thickness of the CaCuO₂. The 2201/SrCuO₂ multilayers do not show a zero electrical resistance above 4.2 K, but the resistance vs. temperature curves present a sharp decrease around 60 K indicative of a superconducting onset.