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Triangular Mott-Hubbard Insulator Phases of Sn/Si(111) and Sn/Ge(111) Surfaces

G. Profeta·E. Tosatti
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Abstract

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.

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G. Profeta, E. Tosatti. 2007-03-07. Triangular Mott-Hubbard Insulator Phases of Sn/Si(111) and Sn/Ge(111) Surfaces. https://doi.org/10.1103/physrevlett.98.086401

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