Scanning tunneling microscope studies on the atomic structures in NdBa2Cu3O7-delta single crystals

Atomic and electronic structures of the cuprate NdBa2Cu3O7-delta (Nd123), w hich is processed by the oxygen-controlled-melt-growth (OCMG) method, have been studied by scanning tunneling microscopy/spectroscopy (STM/STS). Two c haracteristic microstructures, namely, island and striped structures have b een observed, the latter for the first time. The former is a well-known pin ning center in OCMG Nd123. The islands are of a couple of tens of nanometer s in size and are found to be less conductive than the embedding matrix. Th ree 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 b right contrast. The striped band is more conductive than the matrix. The st riped 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 c andidate for another strong pinning center in OCMG Nd123. (C) 2000 Elsevier Science B.V. All rights reserved.