Atomic image of a CuO₂ plane in the STM image of a Bi₂Sr₂CaCu₂O_8+δ cleaved surface

Clear atomic images of a Bi₂Sr₂CaCu₂O_8+δ (BSCCO) cleaved surface were obtained at room temperature by scanning tunneling microscopy (STM). The features of some observed images vary between two extreme cases, that is, the Bi-O plane image and the CuO₂ plane image. And we have succeeded in obtaining a clear STM image of a CuO₂ plane. From the CuO₂ plane image, we found that this plane had two superstructures, one along the a axis and the other along the b axis. The periodicity of the superstructure along the b axis is (4-5)b, the same as that in the Bi-O plane, and the periodicity along the a axis is 2a. To explain these superstructures, we propose a lattice distortion model for the CuO₂ plane of BSCCO.