Low Temperature Physics: 37, 834 (2011); https://doi.org/10.1063/1.3670026 (6 pages)
Fizika Nizkikh Temperatur: Volume 37, Number 9-10 (September 2011), p. 1046-1052 ( to contents , go back )
Manifestation of the Upper Hubbard band in the 2D Hubbard model at low electron density
P.L. Kapitza Institute for Physical Problem, 2 ul. Kosygina, Moscow 119334, Russia
Kirensky Institute of Physics, Akademgorodok, 50, bld. 38, Krasnoyarsk 660036, Russia
Institute for Theoretical Condensed Matter physics, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str., 1, Karlsruhe D-76131, Germany
Received May 10, 2011
We consider the 2D Hubbard model in the strong-coupling case (U >> W) and at low electron density (nd 2 << 1). We find an antibound state as a pole in the two-particle T-matrix. The contribution of this pole in the self-energy reproduces a two-pole structure in the dressed one-particle Green-function similar to the Hubbard-I approximation. We also discuss briefly the Engelbrecht-Randeria mode which corresponds to the pairing of two holes below the bottom of the band for U >> W and low electron density. Both poles produce nontrivial corrections to Landau Fermi-liquid picture already at low electron density but do not destroy it in 2D.
PACS: 71.10.Fd Lattice fermion models (Hubbard model, etc.).
Key words: Hubbard model, Green-function, low electron density.