Destabilization of the Zhang-Rice singlet at optimal doping

Abstract

The construction of the Zhang-Rice singlet is revisited in the light of recent understanding of high-temperature superconductors at optimal doping. A minimal local model is derived which contains the physical regime found relevant for ARPES experiments, characterized by significant direct oxygen-oxygen hopping. For the values of orbital parameters indicated by experiment, the Zhang-Rice singlet is strongly mixed with a pure oxygen singlet of the same symmetry. The destabilization of the Zhang-Rice ground state is due to the oxygen singlet having twice as large a coherence factor with respect to oxygen-oxygen hopping. An analogous quantum phase transition is identified in the t-t ′ -J model. The orbital-antisymmetric copper-oxygen singlet is confirmed to be irrelevant, as found originally. The usual symmetry analysis is extended to include dynamical symmetries.

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

“…By making n d < 1 at fixed x ≈ 0 the hybridization plays, in a sense, the role of an effective electron doping of the Cu-sites. In particular, the additional hole can then go to a given Cu site [1,[12][13][14] even at x = 0. However, two holes have to avoid each other in time since the double occupation of the Cu site is forbidden.…”

“…Second, t 2 pd is reduced in (17) by large U d according to (13). Not surprisingly,Û coh pd is decreased on increasing n HF d , which requires increasing the order of the calculation.…”

“…The HF band is not only renormalized according to (13) and (14), but the reduction factor R of (13) also projects out a fraction of the renormalized HF chargen HF d into the physical charge on the Cu site. This fraction is coming from the coherent states,…”

“…according to (13) and (16). The difference betweenx and x is due to the fact that more charge is associated with incoherent states than what is projected out from the coherent states.…”

In-Plane Oxygens in High-Temperature Superconducting Cuprates

“…Often even further terms are introduced, turning the model dispersion into an effective Fourier-Taylor series, which can easily fit any observed FS [21]. However, when ph-symmetry-breaking terms are properly disentangled [22] from the symmetry-preserving ones, it turns out the correction outweighs the initial term by a factor of 3-8 in realistic fits, because the relevant ratio is |4t ′ /(t + 2t ′ )|, with t ′ /t < 0, not ∼ |t ′ /t|, as one might naively assume. Such dominance of the correction means that the mapping of the three-band onto the one-band dispersion is singular in the physical regime actually observed in the cuprates, as also indicated by unrealistically long-distance hopping terms, amounting to a diverging Taylor series.…”