Nuclear magnetic resonance—a bulk, local probe of materials’ electronic properties—has been significant for theories of high-temperature superconducting cuprates. However, more recent NMR experiments revealed several contradictions in the early interpretation of the NMR data. This cumulative thesis, comprised of six publications, aims to develop a new phenomenology based on the entirety of Cu and O NMR shift and relaxation data.
The data revealed that a suppression of the Cu shifts is behind the failure of the Korringa relation, while the Cu relaxation measured with one direction of the field (c||B0) is similar for all cuprates and is Fermi-liquid like. The Cu shift and relaxation anisotropies could be explained by assuming two-spin components with different doping and temperature dependencies. A later analysis of all planar O shift and relaxation showed that a metallic-like density of states is ubiquitous to all the cuprates, irrespective of doping and material, and carries a temperature-independent but doping-dependent pseudogap, as similarly seen in the electronic entropy.
This temperature-independent pseudogap is behind the suppression of the Cu shifts, but it has no influence on the Cu relaxation. Additionally, the Cu shifts measured with the field perpendicular to the c-axis reveal a family dependence. We propose a two-spin component model, explaining the family dependence in the Cu shifts, the complex Cu shift anisotropy and relaxation, and the disparity in the temperature dependence between the Cu and O shifts. This model also accounts for the missing negative shift and the long-standing Cu orbital shift discrepancy.
While these conclusions are phenomenological, they must be explained by a detailed theory of the cuprate
