Scanning tunneling microscope studies on the atomic structures in NdBa₂Cu₃O_7-δ single crystals

Atomic and electronic structures of the cuprate NdBa₂Cu₃O_7-δ, which is processed by the oxygen-controlled-melt-growth (OCMG) method, have been studied by scanning tunneling microscopy/spectroscopy (STM/STS). Two characteristic microstructures, namely, island and striped structures have been observed, the latter for the first time. The former is a well-known pinning center in OCMG Nd123. The islands are of a couple of tens of nanometers in size and are found to be less conductive than the embedding matrix. Three types of stripes, namely, regular, spotted and irregularly spaced ones, have been observed. The stripe consists of lines of bright contrast and of a few atom rows running parallel to and between the neighboring lines of bright contrast. The striped band is more conductive than the matrix. The striped and flat bands of a couple of tens of nanometers wide each are found to be arranged alternately. We suggest the striped structure to be a good candidate for another strong pinning center in OCMG Nd123.