Clear atomic images of a ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ (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 ${\mathrm{CuO}}_2$ plane image. And we have succeeded in obtaining a clear STM image of a ${\mathrm{CuO}}_2$ plane. From the ${\mathrm{CuO}}_2$ plane image, we found that this plane had two superstructures, one along the $\mathbf{a}$ axis and the other along the $\mathbf{b}$ axis. The periodicity of the superstructure along the $\mathbf{b}$ axis is $(4\mathrm{}–5)\mathbf{b},$ the same as that in the Bi-O plane, and the periodicity along the $\mathbf{a}$ axis is $2\mathbf{a}.$ To explain these superstructures, we propose a lattice distortion model for the ${\mathrm{CuO}}_2$ plane of BSCCO.

• Received 12 January 2000

DOI:https://doi.org/10.1103/PhysRevB.62.8715