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Comparison of the Emery model band structure and the ARPES data for the high - Tc superconductors

The electronic band structure of the interacting Emery model for the high-Tc superconductors is calculated, characterized with three parameters: the site-energy difference D between Cu and O, the Cu-O overlap t and the O-O overlap t&#8217 ; . Strong electron (hole) correlations on the Cu site are treated by infinite U mean-field slave boson approximation, leading to the effectively free electrons with the values of D and t depending on the doping. Performing analytically slave boson renormalisation for the regime D, t >>t', it is shown that the model with small t' maps onto the model with t'=0 with modified values of parameters, in particular the value of bare parameter where Brinkman-Rice metal-insulator transition takes place. This mapping though fails in the region of large bare values of D, for which a perturbative approach to t' is no more valid. Here, the renormalisation of D saturates at 4|t'|, showing that the copper band never crosses the oxygen band, pointing to new, physically important results. These effective band parameters are then used to fit Fermi surfaces and energy bands of LSCO, Bi2212 and Y123, observed in the ARPES experiments. It is shown that the evolution of the Fermi surface with doping, measured in LSCO, can be explained within the above renormalisation scheme, if the underdoped regime is associated with strong renormalisation of t and saturation of D. Doping then increases strongly the value of t with respect to t', while the value of D stays practically unaffected as suggested by slave boson calculation.

extended Emery model; effective band-structure; slave boson renormalization; ARPES

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