Hexagonal phase with mosaic structure of charge-density waves observed by scanning tunneling microscopy at the surface of a NbSe3 crystal

STM study performed al the temperature 4.2 K has shown that a part of the crystal surface of quasi-one-dimensional conductor NbSe3 is covered by a two-dimensional phase with a hexagonal crystal lattice and hexagonal superlattice. Charge-density waves at these areas arrange mosaic structure with a typical domain size around 150 Angstrom and with different orientations of the superlattice wave vectors. Tunnel current-voltage characteristics demonstrate that the observed phase has a Peierls gap in the electron spectra Delta approximate to 80 meV and a negligible density of states at the Fermi level.