STM/STS observations of Co impurities in Bi2.1Sr1.8Ca(Cu1-xCox)2O8+y single crystals

Cleaved surfaces of Bi2.1Sr1.8Ca(Cu1-xCox)(2)O8+y (x = 0.04) have been investigated by STM/STS at cryogenic temperatures. The obtained conductance image, which maps the local density of states (LDOS) near the Fermi level, clearly showed Co impurities present in the CuO2 planes, indicating that the low-energy excitation spectrum is substantially affected by the impurity doping. The site-specified tunneling spectra on both the impurity site and host superconductor region at 66 K revealed a smeared gap-like structure. On the impurity sites, we have found nearly linear background extended up to a sample bias voltage of 1 V, while the background in the host superconductor region was rather flat. The present STM/STS results suggest that the scattering of electrons by magnetic impurities modifies the LDOS in an energy region scaled by J. (C) 2000 Elsevier Science B.V. All rights reserved.