Stripes, pseudogaps, and Van Hove nesting in the three-bandt-Jmodel

Abstract

Slave boson calculations have been carried out in the threeband tJ model for the high-Tc cuprates, with the inclusion of coupling to oxygen breathing mode phonons. Phononinduced Van Hove nesting leads to a phase separation between a hole-doped domain and a (magnetic) domain near half filling, with long-range Coulomb forces limiting the separation to a nanoscopic scale. Strong correlation effects pin the Fermi level close to, but not precisely at the Van Hove singularity (VHS), which can enhance the tendency to phase separation.The resulting dispersions have been calculated, both in the uniform phases and in the phase separated regime. In the latter case, distinctly different dispersions are found for large, random domains and for regular (static) striped arrays, and a hypothetical form is presented for dynamic striped arrays. The doping dependence of the latter is found to provide an excellent description of photoemission and thermodynamic experiments on pseudogap formation in underdoped cuprates. In particular, the multiplicity of observed gaps is explained as a combination of flux phase plus charge density wave (CDW) gaps along with a superconducting gap. The largest gap is associated with VHS nesting. The apparent smooth evolution of this gap with doping masks a crossover from CDW-like effects near optimal doping to magnetic effects (flux phase) near half filling. A crossover from large Fermi surface to hole pockets with increased underdoping is found. In the weakly overdoped regime, the CDW undergoes a quantum phase transition (TCDW → 0), which could be obscured by phase separation.

Phase separation models for cuprate stripe arrays

“…We have suggested that other VHS-stabilized phases are more likely 52 (see also Ref. 53), and here we explore the properties of a Class A CDW phase 48 . At a doping x ∼ 0.25, the effects of correlations are relatively weak, renormalizing the bandwidth by a factor of ∼2.…”

“…The two most common interpretations for the pseudogap are in terms of either precursor pairing or a competing order parameter, which may be magnetic 74,75 or charge-density wave (CDW) 48,76 . We will argue in the next subsection that the latter possibility is more likely.…”

“…(4) Correlation effects due to Hubbard U are neglected: previous slave boson calculations suggest that the main effect is a bandwidth renormalization of a factor ∼2. 48 We briefly recall the energy dispersion and the gap equations of the model 63 , generalized to d-wave. In terms of a function…”

Phase separation in the vicinity of quantum-critical doping concentration: Implications for high-temperature superconductors

“…The horizontal line corresponds to the value of K 0 + K Coul estimated according to formulas (16) and (18) The line corresponding to K η (x c0 ) is obtained using K ηM (x c0 ) given by Eq. (20) with J = 125 meV.…”

“…Theoretically, the general tendency towards phase separation in cuprates and cuprate-related models is extensively discussed in the literature [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30], but any conclusion about the actual presence or absence of phase separation suffers from uncertainties associated with the gross simplifications in the models. The important advantage of the phase separation measure introduced in this work is that it is directly applicable to real materials.…”