Stress induced change in hole concentration in superlattice films of bismuth-based oxide superconductors

Superlattice films of bismuth-based oxide superconductors, for instance (22 34)(1)(2212)(1) and (2245)(1)(2201)(1), have been synthesized by sequential sputter deposition of bismuthoxide, strontium-copper-oxide and calcium-cop per-oxide monolayers. Crystal structures, superconducting transition temper atures and hole concentration of the films were studied by x-ray diffractio n, Meissner effect and Hall effect measurements. It was observed that the s uperconducting transition temperatures were enhanced by forming superlattic e films of over doped (2212, 2201) and under doped (2234, 2245) phases. The results can be understood by stress induced changes in the hole concentrat ion between the over and the under doped phases originated from the epitaxi al (lattice matching) formation of the superlattice films.