INELASTIC NEUTRON-SCATTERING IN CUPRATE SUPERCONDUCTORS - EVIDENCE FOR INHOMOGENEOUS MATERIALS PROPERTIES

There is increasing experimental evidence for the coexistence of diffe rent types of local regions in doped high-T-c superconductors of ''123 '' and ''214'' type. They may be classified into local regions of undo ped, intermediately doped, and highly doped character. The doping mech anism makes the system inhomogeneous, and the superconducting state is reached by a percolation process. Very detailed information about the volume fractions and the spatial extent of the local regions can be o btained by neutron spectroscopic investigations of the crystal-held in teraction at the rare-earth site which is an ideal local probe of the charge distribution in the superconducting copper oxide planes. The in homogeneous materials properties have to be taken into account in any interpretation of the physical properties of doped high-T-c supercondu ctors. This is exemplified for the static and dynamic copper spin corr elations of YBa2Cu3Ox (6 less than or equal to x less than or equal to 7). We show that the spin fluctuations observed in the superconductin g state can be associated with the undoped and intermediately doped re gions of the system, whereas no magnetic scattering occurs for the hig hly doped regions.