Identification of atomic layers of YBa2Cu3O7-delta by scanning tunneling microscopy and spectroscopy

Low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) measurements have been performed on YBa2CU3O7-delta single crystals cleave d below 20K in order to obtain clean surfaces. The observed STM images are classified into two types of atomic images corresponding to BaO and CuO-cha in layers, and the superconducting STS spectra are observed only on the lat ter layer. In the BaO layer, barium atomic images are clearly observed for the first time in addition to oxygen atomic images. In the CuO-chain layer, on the other hand, we observe the oxygen atomic images, in which a number of oxygen vacancies form clusters along the b-axis. Moreover, the CuO-chain layer shows elliptically modulated electronic images which are attributed to the charge density wave in the CuO chains.