  An ideal one-dimensional electronic system is formed along atomic chains on
Au-decorated vicinal silicon surfaces but the nature of its low temperature
phases has been puzzled for last two decades. Here, we unambiguously identify
the low temperature structural distortion of this surface using high resolution
atomic force microscopy and scanning tunneling microscopy. The most important
structural ingredient of this surface, the step-edge Si chains are found to be
strongly buckled, every third atoms down, forming trimer unitcells. This
observation is consistent with the recent model of rehybridized dangling bonds
and rules out the antiferromagnetic spin ordering proposed earlier. The
spectroscopy and electronic structure calculation indicate a charge density
wave insulator with a Z3 topology making it possible to exploit topological
phases and excitations. Tunneling current was found to substantially lower the
energy barrier between three degenerate CDW states, which induces a dynamically
fluctuating CDW at very low temperature.
