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Slave boson description of the CuO2 planes of the high-Tc superconductors

We revise mean-field approximation of slave-boson approach and show that through the consistent treatment of ground state energy and particle-propagators the Luttinger sum rule is preserved. The approximation results with the effectively free electron system where the effects of strong Coulomb interaction are manifested through the renormalization of the band-parameters. Applying this approximation on the extended Emery model for the CuO2 plane of the high-Tc superconductors, electronic band structure, characterized with three parameters: the site-energy difference D between Cu and O, the Cu-O overlap t and the O-O overlap t’ Performing analytically slave-boson renormalisation due to large U on the Cu site, it is shown in the regime D>>t, t', that the model with small t' maps onto the model with t'=0 with modified values of parameters where Brinkman-Rice metal-insulator transition takes place. This mapping fails in the region of large bare values of D, where the renormalized D saturates at 4|t'. The 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 they can be explained within the above renormalisation scheme, if the underdoped regime is associated with strong renormalisation of t and saturation of D.

high-Tc superconductors; slave boson approximation; electronic band-structure; ARPES measurements

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