New Superstructure on the Surface of 2H-NbSe ₂ and Tunneling Spectra at 4.2 K

抄録

The atomic structure and tunneling spectra of a cleaved surface of a 2H-NbSe₂ single crystal were studied by scanning tunneling microscopy at 4.2 K. Small domains with √13 × √13 modulation were found adjacent to the flatsurface with a 3 × 3 intrinsic charge density wave (CDW). The surface atom arrangement in the domains is the same as that in the 2H-type surface.The density of states around the Fermi energy was measured at the domains by tunneling spectroscopy, and found to be lower than that at the 2H-type surface. The √13 × √13 modulation is considered to originate from another CDW, which can be expected to occur in 4H-NbSe₂ clusters buried in a 2H-type crystal. The change of the tunneling spectrum across the boundary between the 2H-typesurface and a √13 × √13 modulated domain was also measured, and the proximity of superconductivity of 2H type to the modulated domain is discussed.