Tight-binding Hamiltonians for high-temperature superconductors and applications to coherent-potential-approximation calculations of the electronic properties of La2−xBaxCuO4−y

Abstract

We present accurate tight-binding parametrizations of the first-principles augmented-plane-wave or linear-augmented-plane-wave band structures of ${\mathrm{LaCuO}}_3$, ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$, ${\mathrm{Ba}}_2$ ${\mathrm{CuO}}_4$, and the high-temperature superconductor ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. We discuss the methodology and efficient application of these fits, including as an example our tight-binding coherent-potential-approximation (CPA) calculations of the effects of disorder on the electronic structure of ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ba}}_{\mathrm{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$. Our CPA calculations support the hypothesis of a rigid-band lowering of the Fermi level for ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ba}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$, enhancing the density of states there. However, for ${\mathrm{La}}_2$ ${\mathrm{BaCuO}}_{4\mathrm{-}\mathrm{y}}$ they yield the interesting result that oxygen vacancies also lower $E_F$ and raise N($E_F$). This is a significant result for the theory of superconductivity in these materials. In addition to CPA calculations, our parametrizations of the band structures should prove to be a useful tool for other studies which will enhance our understanding of these materials.