Electron Correlation and the c-axis Dispersion of Cu dz2: a New Band Structure for High Temperature Superconductors
Abstract
Previously we showed the major effect of electron correlation in the cuprate superconductors is to lower the energy of the Cu dx2-y2/O psigma (x2-y2) band with respect to the Cu dz2/O' pz (z2) band. In our 2D Hubbard model for La1.85Sr0.15CuO4 (LaSCO), the z2 band is narrow and crosses the standard x2-y2 band just below the Fermi level. In this work, we introduce c-axis dispersion to the model and find the z2 band to have considerable anisotropic 3D character. An additional hole-like surface opens up in the z2 band at (0,0,2pi/c) which expands with doping. At sufficient doping levels, a symmetry allowed x2-y2/z2 band crossing along the (0,0)-(pi,pi) direction of the Brillouin zone appears at the Fermi level. At this point, Cooper pairs between the two bands (e.g. (k uparrow x2-y2/k downarrow z2)) can form, providing the basis for the Interband Pairing Theory of superconductivity in these materials.
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