Direct evidence of the charge ordered phase transition of indium nanowires on Si(111)

A controversial issue of the driving force for the phase transition of the one-dimensional (1D) metallic In wires on Si(111) is studied by low-temperature scanning tunneling microscopy and spectroscopy. The energy gap opening and the longitudinal charge ordering through charge transfer at the Fermi level are unambiguously observed. The vacancy defects induce a local charge ordering decoupled from a lattice distortion above T-c, and pin the phase of charge order below T-c. All these results below and above T-c including the detailed features such as local fluctuations strongly support the 1D charge-density-wave mechanism for the phase transition.