First-principles calculations for a CuO 5 pyramid embedded in YBa 2Cu 3O 7− δ and effects of charge density wave on its electronic structure

Abstract

We have performed first-principles cluster calculations by the multi-configuration self-consistent field variational method for CuO 5 pyramid embedded in superconducting YBa 2Cu 3O 7 (YBCO 7) with T c=90 K. In this calculation we have found a remarkable feature in the many-body electronic structure of YBCO 7: the Zhang–Rice singlet and the Hund’s coupling triplet appear alternately under the coexistence of the local antiferromagnetic spin ordering and charge density wave in a Cu–O chain. This is the first theoretical study to have clarified the important role of a Cu–O chain in creating a metallic and superconducting state of YBCO 7.