«FEB MAY MAR » 1 2009 2010 2011 4 captures 13 Feb 10 - 5 Mar 11

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Abstract:
For a strongly correlated metal close to the Mott-Hubbard metal-insulator transition, interesting surface effects can be expected: The reduced surface coordination number implies a reduced variance of the local density of states and thus an enhanced effective Coulomb interaction at the surface. Therefore, near the bulk critical interaction it seems to be plausible to find a Mott insulating surface while the bulk is still metallic. It is shown, however, that such a surface phase is impossible. Rather, the opposite scenario can be realized: a metallic phase at the surface of a bulk Mott insulator. For this purpose the particle-hole symmetric Hubbard model is investigated on a semi-infinite simple-cubic lattice at zero temperature in three and infinite spatial dimensions. Using the dynamical mean-field theory, the U and layer dependence of the quasi-particle weight is calculated. For uniform model parameters the surface quasi-particle weight is found to be significantly reduced. Here a correlation-induced surface state prevents the Mott transition of the surface. A metallic surface phase coexisting with an insulating bulk is obtained for moderate changes of the surface hopping and/or surface U. The phase diagrams for different geometries are discussed and compared with the predictions resulting from a simple linearization of the mean-field equations in the critical regime. The Mott transition can also be driven by varying the thickness of thin films. This is shown by a DMFT calculation of the thickness dependence of the critical interaction for the Hubbard model on simple-cubic film geometries. The results are again compared with those of the linearized theory.