Calculation of the exciton spectrum ofYBa2Cu3O7

Abstract

Starting from the correlation corrected ͑quasiparticle͒ band structures of the CuO 2 plane and the CuO chain ͑always including the apical oxygen atom͒ of YBa 2 Cu 3 O 7 we have calculated the exciton spectra of both systems. For this the intermediate exciton theory was applied in its first-principles form. This leads to a Green's-matrix equation for the determination of the E q exciton energies. We have applied in the denominator of the Green's-matrix quasiparticle one-electron energies instead of the Hartree-Fock ones. In this way we have found very good agreement with experiment for the calculated exciton energies of the CuO 2 plane ͑theoretical values 4.4-5.7 eV, experimental values 4.5-5.5 eV͒. Further there is a reflexion spectrum peak of YBa 2 Cu 3 O 6.9 at 8.0 eV which agrees well with our results obtained for the exciton energies of the chain.

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