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TT: Tiefe Temperaturen

TT 25: Correlated Electrons - Poster Session

TT 25.52: Poster

Mittwoch, 29. März 2006, 14:30–18:30, P1

Energy gap in asymmetric Hubbard model — •Ihor V. Stasyuk and Orest B. Hera — Institute for Condensed Matter Physics, 1 Svientsitskii Street, 79011 Lviv, Ukraine

Energy band structure of the asymmetric Hubbard model with hopping integrals dependent on an electron spin (particle sort) is studied using an approximate analytic method within the dynamical mean-field theory. To solve the single-site problem, we use the equation of motion approach. Irreducible parts are separated by projecting on the basis of Hubbard operators, and are calculated using different-time decoupling. Our approximation is a generalization of the Hubbard-III approximation, and it includes the scattering responsible for the additional mechanism (due to the hopping of particles with different spin) of the band formation. When the single-site Coulomb repulsion U is increased, a gap appears in the spectrum. In the Falicov-Kimball limit (when particles of one sort are localized), our approach gives the exact result for the critical value of U corresponding to the alloy-analogy approximation. When a small nonzero hopping of localized particles is introduced, the spectrum is broadened and that leads to the increase of critical U.