Electron correlation effects at Sn/Si(111)-3x3, root 3x root 3 and Sn/Ge(111)-3x3, root 3x root 3 reconstructions

Electron correlation effects for the two-dimensional electron gas associate d with the surface bands of the Sn/Si(1 1 1)-3 x 3, root3- x root3, Sn/Ge(1 1 1)-3 x 3 and root3 x root3 reconstructions are analyzed. Unrestricted lo cal-density-approximation (LDA) calculations enable to define a many-body h amiltonian that includes intra- and inter-site electron interactions. From the analysis of this hamiltonian, it can be concluded that the root3 x root 3 reconstructions present a Mott transition, while the 3 x 3 surface remain s metallic. How these results can be used to to discriminate between confli cting models explaining the,root3- x root3 --> 3 x 3 phase transition is de scribed. Inverse photoemission data for the Sn/Si(1 1 1) surface suggests t hat this phase transition can be explained by means of a dynamical fluctuat ions model. (C) 2001 Elsevier Science Ltd. All rights reserved.