As a versatile, bulk quantum probe of electronic properties, nuclear magnetic resonance (NMR) must hold key information about the cuprates, and NMR's discovery of the signatures of the pseudogap - i.e. the spin-gap, as it was called early on - evidences its power. However, with reliable theory missing, NMR is notoriously difficult to interpret since it carries a wealth of information. Early on, unfortunately, data for only a few cuprates were available, which - as we will show - led to a flawed interpretation of NMR data. Based on extensive literature analyses of shift and relaxation on a large number of cuprate families, available today, we present a new NMR phenomenology of the cuprates. For example, the pseudogap reveals itself as a temperature independent gap at the Fermi surface set by the doping level (similar to what was inferred from specific heat data). Interestingly, however, the pseudogap is completely absent in planar copper relaxation that is found to be quite ubiquitous, i.e. independent on material and doping. Details of the new phenomenology will be discussed, as well as its relation to the charge sharing in the copper-oxygen plane, which also correlates with the maximum critical temperature and other cuprate properties.
Keywords: pseudogap, cuprate, NMR