title: Fermi condensation near van Hove singularities within the Hubbard model on the triangular lattice.
abstract: The proximity of the Fermi surface to van Hove singularities drastically enhances interaction effects and leads to essentially new physics. In this work we address the formation of flat bands ("Fermi condensation") within the Hubbard model on the triangular lattice and provide a detailed analysis from an analytical and numerical perspective. To describe the effect we consider both weak-coupling and strong-coupling approaches, namely the renormalization group and dual fermion methods. It is shown that the band flattening is driven by correlations and is well pronounced even at sufficiently high temperatures, of the order of 0.1-0.2 of the hopping parameter. The effect can therefore be probed in experiments with ultracold fermions in optical lattices.
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Yudin
authors.affiliation: Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, D-20355 Hamburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hirschmeier
authors.affiliation: Institut de Physique Théorique (IPhT), CEA, CNRS, 91191 Gif-sur-Yvette, France.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Hafermann
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
authors.forename: Olle
authors.initials: O
authors.lastname: Eriksson
authors.affiliation: Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, D-20355 Hamburg, Germany.
authors.forename: Alexander I
authors.initials: AI
authors.lastname: Lichtenstein
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heijendaalseweg 135, NL-6525 AJ Nijmegen, The Netherlands and Department of Theoretical Physics and Applied Mathematics, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia.
authors.forename: Mikhail I
authors.initials: MI
authors.lastname: Katsnelson