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

A derailed tight-binding analysis of the electron band structure of the CuO2 plane of layered cuprates is performed within a a-band Hamiltonian including 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 located in a Cu or O band, respectively, are considered. For these two alternatives, analytical expressions are obtained for the linear combination of atomic orbitals (LCAO) electron wave functions suitable for the treatment of electron superexchange. Simple formulae for the Fermi surface and electron dispersions are derived by applying the Lowdin downfolding procedure to set up the effective copper and oxygen Hamiltonians, They are used to fit the experimental angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) Fermi surface of Pb0.42Bi1.73Sr1.94Ca1.3Cu1.92O8+x, and both the ARPES and local density approximation (LDA) Fermi surface of Nd2-xCexCuO4-delta. The value of presenting the hopping amplitudes as surface integrals of ab initio atomic 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 four transverse pi-orbitals Ru 4d(zx), Ru 4d(yz), O-a 2p(z), Ob 2p(z) are considered separately. It is shown that the equation for the constant-energy curves and the Fermi contours has the same canonical form as the one for the layered cuprates.