The ground state of Sn/Si(111) and Sn/Ge(111) surface α-phases is reexamined theoretically, based on ab−initio calculations where correlations are approximately included through the orbital dependence of the Coulomb interaction (in the local density + Hubbard U approximation). The effect of correlations is to destabilize the vertical buckling in Sn/Ge(111) and to make the surface magnetic, with a metal-insulator transition for both systems. This signals the onset of a stable narrow gap Mott-Hubbard insulating state, in agreement with very recent experiments. Antiferromagnetic exchange is proposed to be responsible for the observed Γ-point photoemission intensity, as well asfor the partial metallization observed above above 60 K in Sn/Si(111). Extrinsic metallization of Sn/Si(111) by, e.g. alkali doping, could lead to a novel 2D triangular superconducting state of this and similar surfaces.
@article{arxiv.cond-mat/0703181,
title = {Triangular Mott-Hubbard Insulator Phases of Sn/Si(111) and Sn/Ge(111) Surfaces},
author = {G. Profeta and E. Tosatti},
journal= {arXiv preprint arXiv:cond-mat/0703181},
year = {2009}
}