Z3 Charge Density Wave of Silicon Atomic Chains on a Vicinal Silicon Surface

TL;DR

This study reveals the low temperature structural distortion of silicon atomic chains on a vicinal silicon surface, identifying a Z3 charge density wave insulator with topological properties and dynamic fluctuations.

Contribution

It provides the first unambiguous atomic-scale imaging of the buckled Si chains and confirms the Z3 charge density wave nature, challenging previous magnetic ordering hypotheses.

Findings

Buckled Si chains form trimer unit cells.

Surface exhibits a Z3 charge density wave insulator.

Tunneling reduces energy barriers, causing dynamic CDW fluctuations.

Abstract

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.