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

Superlattice films of bismuth-based oxide superconductors, for instance (2234)/sub 1/(2212)/sub 1/ and (2245)/sub 1/(2201)/sub 1/, have been synthesized by sequential sputter deposition of bismuth oxide, strontium-copper-oxide and calcium-copper-oxide monolayers. Crystal structures, superconducting transition temperatures and hole concentration of the films were studied by X-ray diffraction, Meissner effect and Hall effect measurements. It was observed that the superconducting transition temperatures were enhanced by forming superlattice films of overdoped (2212, 2201) and underdoped (2234, 2245) phases. The results can be understood by stress induced changes in the hole concentration between the overdoped and the underdoped phases originating from the epitaxial (lattice matching) formation of the superlattice films.