DESTABILIZATION OF THE ZHANG-RICE SINGLET AT OPTIMAL DOPING
Sunko D.K.

Received: November 10, 2008

PACS: 74.72.-h, 74.25.Jb, 71.10.Hf

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The construction of the Zhang-Rice singlet is revisited in the light of the recent understanding of high-temperature superconductors at optimal doping. A minimal local model is derived that contains the physical regime found relevant for ARPES experiments and 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 Zhang-Rice ground state is destabilized because the coherence factor of the oxygen singlet with respect to oxygen-oxygen hopping is twice as large. 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.