In-Plane Rotated Crystal Structure in Continuous Growth of Bismuth Cuprate Superconducting Film

Bismuth cuprate superconductor has a unique structure called a structural modulation (supercell, SC) consisting of modulated several unit cells. Strain induced by multilayered structure increases the intensity of SC modulation, while an oxygen deficient sample shows expansion of SC size. In this study, as opposed to the multilayer strain, by preparing samples with thick film thicknesses the effect of strain on crystal structure was investigated including SC structure. Epitaxial growth was verified by x-ray diffraction, and the thicker film showed other epitaxial phase rotated 32° around the surface normal with respect to the initial epitaxial phase. The SC size estimated by x-ray reciprocal space mapping was double the size of the initial epitaxial phase. Interestingly, the initial epitaxial phase became a dominant structure after further deposition. In order to evaluate the different SC size and SC modulation, a new index related with an incline of the modulation vector was proposed.