Neutron scattering study of the antiferromagnetic response of HgBa$_{\mathrm{2}}$CuO$_{\mathrm{4+\delta }}$

Antiferromagnetic correlations have been argued to be the cause of the $d$-wave superconductivity and of the pseudogap phenomena exhibited by the cuprates. Although neutron scattering experiments of the antiferromagnetic response have been reported for a number of cuprates, results for structurally simple HgBa$_{\mathrm{2}}$CuO$_{\mathrm{4+\delta }}$ (Hg1201) have begun to emerge only recently. Specifically, we have found for moderately-doped Hg1201 ($T$c $\approx $ 71 K, pseudogap temperature $T$* $\approx $ 305 K) that the two most prominent features of the magnetic spectrum reported for other cuprates are absent: the X-shaped `hourglass' response and the resonance mode in the superconducting state. Instead, the response of Hg1201 is Y-shaped, gapped, and significantly enhanced below $T$* [1]. Here we will discuss our ongoing efforts to understand the doping dependence of the AF response in Hg1201. [1] M. K. Chan \textit{et al., }arXiv:1402.4517.