Localized modes in one-dimensional (1D) topological systems, such as Majonara modes in topological superconductors, are promising candidates for robust information processing. While theory predicts mobile integer and fractional topological solitons in 1D topological insulators, experiments so far have unveiled immobile, integer solitons only. Here we observe fractionalized phase defects moving along trimer silicon atomic chains formed along step edges of a vicinal silicon surface. By means of tunnelling microscopy, we identify local defects with phase shifts of 2π/3 and 4π/3 with their electronic states within the band gap and with their motions activated above 100 K. Theoretical calculations reveal the topological soliton origin of the phase defects with fractional charges of ±2e/3 and ±4e/3. Additionally, we create and annihilate individual solitons at desired locations by current pulses from the probe tip. Mobile and manipulable topological solitons may serve as robust, topologically protected information carriers in future information technology.

We demonstrate using scanning tunneling microscopy and spectroscopy the electron quantization within metallic Au atomic wires self-assembled on a Si(111) surface and segmented by adatom impurities. The local electronic states of wire segments with a length up to 10 nm are investigated as terminated by two neighboring Si adatoms. One dimensional (1D) quantum well states are well resolved by their spatial distributions and the inverse-length-square dependence in their energies. The quantization also results in the quantum oscillation of the conductance at the Fermi level. These results deny the dopant role of the adatoms assumed for a long time but indicate their strong scattering nature. The present approach provides a new and convenient platform to investigate 1D quantum phenomena with atomic precision.One-dimensional (1D) materials systems have been investigated extensively because both of the intriguing and exotic nature of their electrons and of the interest in nano or atomic scale devices. Characteristic 1D electronic properties of fundamental interest include the TomonagaLuttinger liquid [1,2], the charge-density wave [3,4], the unconventional superconductivity [5], and more recently, Majorana Fermions [6,7]. However, 1D materials systems are notorious in their intrinsic susceptibility to extrinsic perturbations such as defects and impurities [8][9][10]. In microscopic points of view, defects or impurities can have various different actions; local or global doping, local lattice distortions, weak or strong electron scatterings and so on. Nevertheless, the direct atomic scale investigation on those actions has been far from being sufficient.The self-assembled atomic wire structure of the Si(111)5×2-Au surface is an excellent candidate system for a systematic study on the interactions of impurities with atomic scale precision. This system has a wellordered Au-Si atomic wire array with a well-defined 1D metallic band [11]. Its atomic structure has been debated for a long time but very recently determined conclusively [12,13]. This surface is intrinsically endowed with Si adatom impurities ejected from the Si substrate [14,15], whose density can be controlled globally [11] or in the atom-by-atom fashion [16]. The electronic band structure is systematically tuned by the adatom density from a metal to a gapped insulator globally [11] or locally [17]. This controllability opens up an unprecedented possibility for a systematic study of impurity effects in an atomic scale 1D metallic system [18].For quite a long time, a Si adatom on this model 1D system was believed to act as a charged impurity [19] and a recent scanning tunneling microscopy and spectroscopy (STM/S) work claimed the observation of the local 'confined' doping effect of individual adatoms [20]. Within this picture, an impurity atom act only to locally shift the energy of the 1D metallic state while the electron scattering and the Friedel oscillation [21] by the impurity are totally neglected. In this work, we focus on the electron scattering by a Si a...

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 puzzling 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 atom down, forming trimer unit cells. 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 Z 3 topology, making it possible to exploit topological phases and excitations. The 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.