Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2007-03-07
Phys. Rev. Lett. 98, 086401 (2007)
Physics
Condensed Matter
Strongly Correlated Electrons
4 pages, 4 figures
Scientific paper
10.1103/PhysRevLett.98.086401
The ground state of Sn/Si(111) and Sn/Ge(111) surface $\alpha$-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 $\Gamma$-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.
Profeta Gianni
Tosatti Erio
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