NMR and electronic inhomogeneity in cuprate superconductors

The issue of electronic inhomogeneity in the cuprate high-temperature superconductors is of great interest as it has implications for interpretation of experiments and for theory. NMR is a very versatile method and we show that the NMR data clearly reveal that all cuprates, although to a very different extent, show inhomogeneity in the static charge and spin density. While part of the evidence makes this inhomogeneity appear to be a variation of local doping, other NMR experiments show that the length-scales involved must be on the order of a few Cu–Cu distances. Estimates of the extent of these variations in different materials are given.