Creation and annihilation of mobile fractional solitons in atomic chains

Jae Whan Park,Jin Sung Shin,Han Woong Yeom,Oleksandr Stetsovych,Sun Kyu Song,Euihwan Do,Pavel Jelinek

doi:10.1038/s41565-021-01042-8

Abstract

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.

Highlights

Localized modes in one-dimensional (1D) topological systems, such as Majonara modes in topological superconductors, are promising candidates for robust information processing
A close electronic example available is that of phase defects in finite size artificial lattices based on a 2D surface state and adsorbates[46]
This system only provides the static modulation of hopping amplitudes for an electronic orbital well away from the Fermi level to preclude the motion and charge fractionalization. These phase defects do not feature the dynamic nature, which is essential to a soliton

Summary

Introduction

Localized modes in one-dimensional (1D) topological systems, such as Majonara modes in topological superconductors, are promising candidates for robust information processing. We observe fractionalized phase defects moving along trimer silicon atomic chains formed along step edges of a vicinal silicon surface. By adsorption of a proper amount of gold atoms, a regular array of step-edge silicon chains is stabilized with unsaturated dangling bonds This system was found to transit into a trimer structure below about 200 K (refs.38–40) and the existence of the phase defects was noticed with their mobility and topological nature unknown[39,41,42]. We observe two different types of soliton with fractionalized (2π/3 and 4π/3) phase shifts, respectively, which are immobile at low temperature but their motion occurs above 100 K Their solitonic property is confirmed by their in-gap electronic states and their immunity for scattering. What concerns the present work are step-edge Si atoms with dangling bonds, which correspond to one side of the Si honeycomb chain

Methods

Conclusion