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Nuclear magnetic resonance (NMR) provides local, bulk information about theelectronic properties of materials, and it has been influential for theory ofhigh-temperature superconducting cuprates. Importantly, NMR found early thatnuclear relaxation is much faster than what one expects from coupling tofermionic excitations above the critical temperature for superconductivity($T_{\rm c}$), i.e. what one estimates from the Knight shift with the Korringalaw. As a consequence, special electronic spin fluctuations have been invoked.Here, based on literature relaxation data it is shown that the electronicexcitations, to which the nuclei couple with a material and doping dependentanisotropy, are rather ubiquitous and Fermi liquid-like. A suppressed NMR spinshift rather than an enhanced relaxation leads to the failure of the Korringalaw for most materials. Shift and relaxation below $T_{\rm c}$ support the viewof suppressed shifts, as well. A simple model of two coupled electronic spincomponents, one with $3d(x^2-y^2)$ orbital symmetry and the other with anisotropic $s$-like interaction can explain the data. The coupling between thetwo components is found to be negative, and it must be related to the pseudogapbehavior of the cuprates. We can also explain the negative shift conundrum andthe long-standing orbital shift discrepancy for NMR in the cuprates.

Properties of the electronic fluid of superconducting cuprates from $^{63}$Cu NMR shift and relaxation