NMR Shift and Relaxation and the Electronic Spin of Superconducting Cuprates

Abstract

Very recently, by inspecting large sets of data across all families of superconducting cuprates, it became obvious that the prevailing nuclear magnetic resonance (NMR) interpretation of cuprate properties is not adequate, as it does not account for the differences between the families, as well as common characteristics beyond simple temperature dependence. From the most abundant planar Cu shift data, one concludes readily on two electronic spin components with different doping and temperature dependencies. Their uniform response that causes NMR spin shifts consists of a doping-dependent component due to planar O, and another due to spin in the planar copper 3d(x2 − y2) orbital, where the latter points opposite the field direction. Planar Cu relaxation was found to be rather ubiquitous (except for La2−xSrxCuO4), and Fermi liquid-like, i.e., independent of doping and material, apart from the sudden drop at the superconducting transition temperature, Tc. Only the relaxation anisotropy is doping and material dependent. We showed previously that one can understand the shifts within a two-component scenario, but we failed with a model to account for the relaxation. Here, we suggest a slightly different shift scenario, still based on the two components, by introducing different hyperfine couplings, and, importantly, we are able to account for the Cu nuclear relaxation and its anisotropy for all materials, including also La2−xSrxCuO4. The results represent a solid framework for theory.