Electronic state of NbSe2 investigated by STM/STS

Scanning tunneling microscopy/spectroscopy and resistivity (rho) measurements were performed on NbSe2 single crystals in which superconductivity and charge-density wave (CDW) coexist. We found a close correlation between residual resistivity ratio (RRR) and the resistive anomaly at the CDW transition, namely, RRR increases when the resistive anomaly becomes clearer. Topographic images at 4.4 K show 3 x 3 CDW superposed on atomic corrugations. Number of CDW domain boundary increases with decreasing RRR, while the CDW image and the tunneling spectrum within each domain are almost independent of RRR. Such a domain structure may reduce the anisotropy in the superconducting state. (C) 2003 Elsevier Science B.V. All rights reserved.