Identification of Atomic Layers of YBa₂Cu₃O_7-δby Scanning Tunneling Microscopy and Spectroscopy

Abstract

Low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) measurements have been performed on YBa 2 Cu 3 O 7-δ single crystals cleaved below 20 K in order to obtain clean surfaces. The observed STM images are classified into two types of atomic images corresponding to BaO and CuO-chain layers, and the superconducting STS spectra are observed only on the latter 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.