What is the role of the oxygen atoms of the CuO chains in the high- T c superconductivity of YBa 2Cu 3O 7−δ?

Abstract

For the YBa 2Cu 3O 7 and YBa 2Cu 3O 6 systems ab initio Hartree-Fock cluster calculations have been performed using a self consistent Madelung potential for the rest of the crystal and periodic boundary conditions. Surprisingly the charge transferred (∼1.0 e) to the CuO 2YCuO 2 subsystem and the charge distribution there show no changes by removal of an oxygen atom from the CuO chain. This points besides chain-superconductivity (which is verified by recent experiments) also to the possibility that the well established hole superconductivity in the CuO 2 planes of (1 2 3) may not originate from hole doping from the CuO chains. Experimental conductivity measurements in the normal state of the (1 2 3) system shows also that the charge transport occurs dominantly along the chain directions.