Single-particle properties of the Hubbard model in a novel three-pole approximation

Abstract

We study the 2D Hubbard model using the Composite Operator Method within a novel three-pole approximation. Motivated by the long-standing experimental puzzle of the single-particle properties of the underdoped cuprates, we include in the operatorial basis, together with the usual Hubbard operators, a field describing the electronic transitions dressed by the nearestneighbor spin fluctuations, which play a crucial role in the unconventional behavior of the Fermi surface and of the electronic dispersion. Then, we adopt this approximation to study the single-particle properties in the strong coupling regime and find an unexpected behavior of the van Hove singularity that can be seen as a precursor of a pseudogap regime.

Controllable precision of the projective truncation approximation for Green’s functions

“…There are other ways of selecting basis operators. [41] Especially, the selection of orthogonal basis operators in the Krylov subspace produces a continued fraction form for the local GF. [8,9] The self-energy functions from pHIA and pAAA in this work have the extended continued fraction form [35] used to do resummation for 047102-8 the strong-coupling series expansions of GF.…”