  We investigated phase defects in a quasi-one-dimensional commensurate charge
density wave (CDW) system, an In atomic wire array on Si(111), using low
temperature scanning tunneling microscopy. The unique four-fold degeneracy of
the CDW state leads to various phase defects, among which intrinsic solitons
are clearly distinguished. The solitons exhibit a characteristic variation of
the CDW amplitude with a coherence length of about 4 nm, as expected from the
electronic structure, and a localized electronic state within the CDW gap.
While most of the observed solitons are trapped by extrinsic defects, moving
solitons are also identified and their novel interaction with extrinsic defects
is disclosed.
