Spin Chains and Electron Transfer at Stepped Silicon Surfaces

TL;DR

This study combines theory and experiments to understand spin polarization in silicon gold surface step edges, revealing conditions for creating and controlling silicon spin chains for potential applications.

Contribution

It introduces an electron-counting model explaining spin polarization differences among similar silicon gold surfaces and demonstrates how defects and dopants can induce local spin moments.

Findings

Si(775)-Au has zero spin polarization at the step edge.

Defects and dopants can create local spin moments.

The model predicts controllable spin chain formation.

Abstract

High-index surfaces of silicon with adsorbed gold can reconstruct to form highly ordered linear step arrays. These steps take the form of a narrow strip of graphitic silicon. In some cases - specifically, for Si(553)-Au and Si(557)-Au - a large fraction of the silicon atoms at the exposed edge of this strip are known to be spin-polarized and charge-ordered along the edge. The periodicity of this charge ordering is always commensurate with the structural periodicity along the step edge and hence leads to highly ordered arrays of local magnetic moments that can be regarded as "spin chains". Here, we demonstrate theoretically as well as experimentally that the closely related Si(775)-Au surface has - despite its very similar overall structure - zero spin polarization at its step edge. Using a combination of density-functional theory and scanning tunneling microscopy, we propose an electron-counting model that accounts for these differences. The model also predicts that unintentional defects and intentional dopants can create local spin moments at Si(hhk)-Au step edges. We analyze in detail one of these predictions and verify it experimentally. This finding opens the door to using techniques of surface chemistry and atom manipulation to create and control silicon spin chains.