Tight-binding modelling of the electronic band structure of layered superconducting perovskites

A derailed tight-binding analysis of the electron band structure of the CuO 2 plane of layered cuprates is performed within a a-band Hamiltonian includ ing four orbitals-Cu 3d(x2)-(y2) and Cu 4s, O 2p(x), and O 2p(y),. Both the experimental and theoretical indications in favour of a Fermi level locate d in a Cu or O band, respectively, are considered. For these two alternativ es, analytical expressions are obtained for the linear combination of atomi c orbitals (LCAO) electron wave functions suitable for the treatment of ele ctron superexchange. Simple formulae for the Fermi surface and electron dis persions are derived by applying the Lowdin downfolding procedure to set up the effective copper and oxygen Hamiltonians, They are used to fit the exp erimental angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) Fer mi surface of Pb0.42Bi1.73Sr1.94Ca1.3Cu1.92O8+x, and both the ARPES and loc al density approximation (LDA) Fermi surface of Nd2-xCexCuO4-delta. The val ue of presenting the hopping amplitudes as surface integrals of ab initio a tomic wave functions is demonstrated as well. The same approach is applied to the RuO2 plane of the ruthenate Sr2RuO4. The LCAO Hamiltonians including the three in-plane pi-orbitals Ru 4d(xy), O-a 2p(y), O-b 2p(x) and the fou r transverse pi-orbitals Ru 4d(zx), Ru 4d(yz), O-a 2p(z), Ob 2p(z) are cons idered separately. It is shown that the equation for the constant-energy cu rves and the Fermi contours has the same canonical form as the one for the layered cuprates.