Local variations of superconducting states in high J(c) NdBa2Cu3Oy single crystals probed by low temperature scanning tunneling spectroscopy

We report scanning tunneling spectroscopy on high J(c) NdBa2Cu3Oy (Nd123) s ingle crystals at cryogenic temperatures below T-c. At 4.2 K, the supercond ucting gap edges were almost constant (2 Delta (pp) similar to 50 mV) over the observed areas up to 80 x 80 nm(2). In contrast, we found spatial regio ns with sizes of a few nanometers, where local density of states (LDOS) ins ide the gap was slightly raised with a subtle peak near the Fermi level, po ssibly reflecting quasi-particle scattering around atomic-scale defects, su ch as oxygen disorders. The enhancement of in-gap LDOS is more prominent at 63 K, suggesting that the corresponding regions act as effective pinning c enters particularly at higher temperatures. (C) 2001 Elsevier Science B.V. All rights reserved.