SPECTRAL FUNCTION OF A d-p HUBBARD MODEL

Abstract

This work investigates a d-p Hubbard model by the n-pole approximation in the hole-doped regime. In particular, the spectral function A(ω, k) is analyzed varying the filling, the local Coulomb interaction and the d − p hybridization. It should be remarked that the original n-pole approximation (Phys. Rev. 184 (1969) 451) has been improved in order to include adequately the k-dependence of the important correlation function Sj · Si present in the poles of the Green's functions. It has been verified that the topology of the Fermi surface (defined by A(ω = 0, k)) is deeply affected by the doping, the strength of the Coulomb interaction and also by the hybridization. Particularly, in the underdoped regime, the spectral function A(ω = 0, k) presents very low intensity close to the anti-nodal points (0, ±π) and (±π, 0). Such a behavior produces an anomalous Fermi surface (pockets) with pseudogaps in the region of the anti-nodal points. On the other hand, if the d − p hybridization is enhanced sufficiently, such pseudogaps vanish. It is precisely the correlation function Sj · Si present in the poles of the Green's functions which plays the important role in the underdoped situation. In fact, antiferromagnetic correlations coming from Sj · Si strongly modify the quasi-particle band structure. This is the ultimate source of anomalies in the Fermi surface in the present approach. IntroductionMore than two decades after the discovery of the cuprates [1], the theoretical description of this phenomenon still represents a challenge for the physicists. The fundamental aspects of the cuprates phase diagram can be described in the following terms. In the overdoped regime, there is a conventional normal metal, *

Specific heat of a non-local attractive Hubbard model

“…The right panel in figure 1 shows that | S i • S j | is large at low temperatures and increases with |G|. As discussed in references [5,6,15], the S i • S j modify the renormalized band structure by enlarging the flat region near the anti-nodal points It is interesting to note that the specific heat presents a peak just at k B T = 0.2|t| and a local minimum at k B T = 0.4|t| (see figure 1). This occurs because at low temperatures the function f…”

“…The right panel in figure 1 shows that | S i · S j | is large at low temperatures and increases with |G|. As discussed in references [5,6,15], the S i · S j modify the renormalized band structure by enlarging the flat region near the anti-nodal points (π, 0) and (0, π). As a consequence, a pronounced peak emerges on the density of state.…”

Superconductivity in an extended Hubbard model with attractive interaction

“…Further decrease in δ intensifies the presence of the pseudo-gap as shown in (c)-(d). This unusual behaviour is due to the strong antiferromagnetic correlations coming from the band shift W d kσ [7,14] defined in equation (A7). The effects described above, are corroborated by the quasiparticle band calculation exhibited in figure 2 which displays the quasiparticle band for distinct doping values δ.…”

“…Further decrease in δ intensifies the presence of the pseudo-gap as shown in (c) and (d). This unusual behavior is due to the strong antiferromagnetic correlations coming from the band shift W d kσ (see [7,14]) defined in equation (A.7).…”