On the nature of antiferromagnetism in the CuO $ \mathsf {_2}$ planes of oxide superconductors

Abstract

SummaryRecent results on electrons and holes doped CuO 2 planes confirm the marked covalency of CuO bonding, suggesting a band picture of long and short range antiferromagnetism. The maxima of superconductive T c versus doping can be related to the crossing by the Fermi level of the edges of the pseudogap due to antiferromagnetic short range order (bonding edge for holes doping, antibonding one for electrons doping). The symmetry of the superconductive gap can be related to the Bragg scattering of electronic Bloch states near the edges of the AF pseudogap. Assuming a standard phonon coupling, one then predicts for commensurate AF a pure d symmetry of the superconductive gap for underdoped samples and d symmetry plus an ip contribution increasing linearly with overdoping. This seems in agreement with recent measurements of gap symmetry for YBCO, but should be more fully tested, especially for electron doped samples. The simple band approximation used here could no doubt be made more realistic by a specific inclusion of electron correlations and by a better description of AF short range order. Uncommensurate AF, as in LSCO, is not considered here. ______

In-plane optical features of the underdoped La2CuO4 based compounds: theoretical multiband analysis

“…The lower doping, the stronger effective perturbation has to be, in full agreement with the conclusion of a similar single-band analysis focused on the characteristic AF energy, given in Ref. [45], and with the related specific heat measurements [46]. A significant deviation from such doping dependence of ∆ 0 is expected for t pp comparable to t pd , or for t pp ≈ ∆ 0 > µ − ε vH .…”

Approaching Large U d High-T c Cuprates from the Covalent Side

“…As pointed out before [17],Ũ hh is the kinematic interaction in the sense that it describes the decrease ofŨ hh with respect toŨ due to the energetic cost of the simultaneous occupation of the copper site. Actually, a similar idea was put forward by Cooper for small retarded attractive interactions V (bosonic glue [19]) characterized by the high frequency cut-off ω D < ε f .…”

“…It was addressed before [17] in a way relevant for the present discussion following the Kanamori approach [18] to transition metals. The propagation of two additional holes with opposite spins is considered in presence of 1+x permanent holes (of both spins).…”

“…The propagation of two additional holes with opposite spins is considered in presence of 1+x permanent holes (of both spins). The effective repulsion between the two holes in question is then given by an S-matrix calculation as [17] …”

“…The propagation of hole-hole and electron-hole pairs is decoupled then on the parquet level, similarly to what happens in quasi 1d conductors with imperfect nesting [26]. The evaluation of magnetic correlations from (8) or the calculations which improve [27,28] this equation amount then to theŨ →Ũ hh mapping [17] of the covalent 3-band theory on the popular weak coupling t, t , U single band model.…”