Artificial high temperature superconducting structures.

(BaCuO2+?)m/(CaCuO2)2 superconducting artificial structures were synthesized by layer by layer pulsed laser deposition. The interlayer coupling between adjacent superconducting CaCuO2 blocks was investigated. The thickness of the BaCuO2+? charge reservoir (CR) layer was gradually increased up to m=10. It was found that interlayer coupling is not essential for high Tc superconductivity: giant CR blocks, thicker than 20 Å, (m ? 5), depress only moderately Tc while increase the 2D character of superconductivity. Furthermore hetero-epitaxial (BaCuO2+?)m/(CaCuO2)2/ (BaCuO2+?)m tri-layers made of a single superconducting block sandwiched between two CR blocks were deposited. Electrical transport measurements showed that such ultra thin structures are superconducting with Tc up to about 60 K and critical current densities (at 4 K) as high as 108 A cm-2. Such finding confirmed the occurrence of purely intralayer superconductivity in these artificial structures.