Antiferromagnetic superexchange mediated by a resonant surface state in Sn/Si(111)

Abstract

The Sn overlayer on the Si(111) surface has been considered as a prototypical system for exploring two-dimensional (2D) correlated physics on the triangular lattice. Most of the previous theoretical studies were based on the presumption that the surface state dominantly originates from Sn dangling-bond (DB) electrons, leading to a strongly correlated 2D electronic system. By contrast, our density-functional theory calculations show that the Sn DB state significantly hybridizes with Si substrate states to form a resonant state. The strong resonance between the Sn 5p(z) and Si 3p(z) orbitals facilitates the recently observed antiferromagnetic order through superexchange interactions, giving rise to a band-gap opening. It is thus demonstrated that the insulating ground state of Sn/Si(111) can be characterized as a Slater-type insulator via band magnetism.