Electronic spin susceptibilities and superconductivity in HgBa₂CuO_(4+δ) from nuclear magnetic resonance

Nuclear magnetic resonance (NMR) experiments on single crystals of HgBa$_{2}$CuO$_{4+\delta}$ are presented that identify two distinct temperature-dependent spin susceptibilities: one is due to a spin component that is temperature-dependent above the critical temperature for superconductivity ($T_{\rm c}$) and reflects pseudogap behavior; the other is Fermi-liquid-like in that it is temperature independent above $T_{\rm c}$ and vanishes rapidly below $T_{\rm c}$. In addition, we demonstrate the existence of a third, hitherto undetected spin susceptibility: it is temperature independent at higher temperatures, vanishes at lower temperatures (below $T_0\neq T_{\rm c}$), and changes sign near optimal doping. This susceptibility either arises from the coupling between the two spin components, or it could be given by a distinct third spin component.