Nuclear magnetic resonance (NMR) experiments on single crystals of ${\mathrm{HgBa}}_2{\mathrm{CuO}}_{4+\delta }$ 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 ($T_{\mathrm{c}}$) and reflects pseudogap behavior; the other is Fermi-liquid-like in that it is temperature independent above $T_{\mathrm{c}}$ and vanishes rapidly below $T_{\mathrm{c}}$. In addition, we demonstrate the existence of a third spin susceptibility: It is temperature independent at higher temperatures, vanishes at lower temperatures (below $T_0\ne T_{\mathrm{c}}$), 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. Recent susceptibility data on single crystals support its presence in most cuprates.

• Received 17 April 2015

DOI:https://doi.org/10.1103/PhysRevB.92.081115