Origin of dz2 orbital suppression of d-wave superconductive pairs in cuprate

Compared to Hg-cuprate, the origin that the d(z2) orbital suppresses the d-wave superconductive (SC) pairs in La-cuprate is studied based on an effective two orbital t-J-U model by using the Kotliar-Ruckenstein (KR) slave-boson technique. By analyzing the orbital-dependent electron distribution, it is elaborated that the double occupancy of d(x2-y2) orbital, caused by the d(z2) orbital mixture, should be responsible for the suppression of the d-wave SC pairs in La-cuprate. When the Coulomb interaction U increases, the ground state hosting the large double occupancy of d(x2-y2) orbital in La-cuprate is stabilized by the localization of the carriers due to the Coulomb-blocking instead of reducing the double occupancy by the way of lowering of Coulomb potential energy. Therefore, it could be concluded that the mechanism that the double occupancy destructs against d-wave SC pairs is robust even if the strong Coulomb interaction exists in the La based compounds. (C) 2015 Elsevier B.V. All rights reserved.