Evidence for Long-Range Spin Order Instead of a Peierls Transition in Si(553)-Au Chains

TL;DR

This study provides evidence that the low-temperature periodicities in Si(553)-Au chains are due to long-range spin order rather than Peierls instabilities, challenging previous interpretations.

Contribution

The paper demonstrates through STM and DFT that the observed superstructures are caused by spin order, not Peierls distortions, offering a new understanding of the surface physics.

Findings

X3 superstructure of Si chains vanishes near the Fermi level

Au chains remain metallic despite period doubling

Results align with density-functional theory predictions of spin-polarized Si atoms

Abstract

Stabilization of the Si(553) surface by Au adsorption results in two different atomically defined chain types, one of Au atoms and one of Si. At low temperature these chains develop two- and threefold periodicity, respectively, previously attributed to Peierls instabilities. Here we report evidence from scanning tunneling microscopy that rules out this interpretation. The x3 superstructure of the Si chains vanishes for low tunneling bias, i.e., close the Fermi level. In addition, the Au chains remain metallic despite their period doubling. Both observations are inconsistent with a Peierls mechanism. On the contrary, our results are in excellent, detailed agreement with the Si(553)-Au ground state predicted by density-functional theory, where the x2 periodicity of the Au chain is an inherent structural feature and every third Si atom is spin-polarized.