Spin density and form factor measurements on HTSC copper oxides

Abstract

Polarized neutron investigations on superconducting copper oxides, La 2− x Sr x CuO 4 and YBa 2Cu 3O 6+ x , as well as studies of related antiferromagnetic compounds, using unpolarized neutrons, permit some of the characteristic features of the spin distribution to be outlined. No covalency on the in-plane oxygen atoms is observed, neither in the antiferromagnetic state, nor in the superconducting state. In superconducting compounds, the in-plane copper displays a small induced magnetic moment, about 10 −3μ B ( H=5T), which is almost independent of temperature. In YBa 2Cu 3O 6+ x , a distinct behaviour is found for the in-chain copper. The induced spin density in HoBa 2Cu 3O 7 exhibits specific features that are not present in non-superconducting HoBa 2Cu 3O 6.5.