Magnetic resonance in the model high-temperature superconductor HgBa 2 CuO 4 + δ

Inelastic neutron-scattering measurements of single-${\text{CuO}}_{2}$-layer ${\text{HgBa}}_{2}{\text{CuO}}_{4+\ensuremath{\delta}}$ reveal an antiferromagnetic resonance with energy ${\ensuremath{\omega}}_{\text{r}}=56\text{ }\text{meV}$ $(\ensuremath{\approx}6.8{k}_{\text{B}}{T}_{\text{c}})$ below the superconducting transition temperature ${T}_{\text{c}}\ensuremath{\approx}96\text{ }\text{K}$. The resonance is energy-resolution limited and exhibits an intrinsic momentum width of about $0.2\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$, consistent with prior work on several other cuprates. The rather large value of ${\ensuremath{\omega}}_{\text{r}}$ is identical to the characteristic energy of the electron-boson spectral density obtained from recent optical conductivity work, consistent with the notion that the charge carriers are strongly coupled to magnetic fluctuations.