Evidence of a new magnetic flux pinning center in Nd1Ba2Cu3Oy single crystals

Highly flat, clean, and stable surfaces of as-prepared Nd1Ba2Cu3Oy (Nd123) single crystals have been studied using an ultrahigh vacuum scanning tunnelling microscope/spectroscopy (UHV-STM/ STS) system. The results of large area STM scans together with the results of STS measurements, magnetization loops measured at several temperatures below T-c, and critical current density measurements reveal the presence of a new magnetic Aux pinning center in Nd123 single crystals prepared in a reduced oxygen partial pressure. This pinning center is more conductive on the surface than the matrix and has a size ranging from several to several lens of nanometers as seen by STM. Similar pinning center may be introduced to other high temperature superconductors to increase their critical current densities in an applied magnetic field. (C) 1997 American Institute of Physics.