HIGH-TC SUPERCONDUCTING ARTIFICIAL LATTICE AS A NEW MATERIAL

High Tc superconducting artificial lattices have been constructed by a layer-by-layer laser molecular beam epitaxy method with atomic layer and sub-unit cell accuracy, and the basic structural factors in the high Tc cuprates have been controlled artificially. In the Bi2Sr2Can-1CunO2n+4 artificial lattices, the numbers of CuO2 planes are changed from one to even eight in the unit formula. The compression and expansion of the CuO2 plane are demonstrated in the strained superlattices of YBa2Cu3O7/(La,Sr)2CuO4 and (La,Sr)2CuO4/Sm2CuO4. In these superlattices, the change of the lattice constant along a,b axes is proved to be one of the important controlling factors in the high Tc cuprates. This technique has been also applied to obtain reliable tunneling spectra of Au/Bi2Sr2CuO6/Bi2Sr2CaCu2O8, and reproducible BCS-like spectra have been obtained in this system. The results indicate that the high Tc cuprate is essentially the BCS superconductor.