Geometrical frustration and the competing phases of the Sn/Si(111) √3 x √3R30° surface systems

We investigate the electronic correlation effects on the Sn/Si(111) root 3 x root 3R30 degrees surface by combining the ab initio density-functional approach with the dynamical mean-field theory, the variational cluster approach, and the dual fermion (DF) method. A metal-insulator transition with first or second order at finite or zero temperature is predicted at a critical on-site Hubbard U(c) similar to 0.65 eV and the system is proven to be short-range correlated. The electron-electron interaction favors a row-wise antiferromagnetic (RW-AFM) order, although the noninteracting system does not have a pronounced nesting at the Fermi surface. The stabilization of the RW-AFM order over the 120 degrees AF one for certain interaction strengths is shown to be due to the longer-range single-particle hopping terms.