Doping dependence of antiferromagnetic correlations in the simple-tetragonal cuprate superconductor HgBa₂CuO_4+δ

The origin of superconductivity in the cuprates, particularly the superconducting pairing mechanism and the role of antiferromagnetic (AF) fluctuations, remains a major unsolved problem in condensed-matter physics. Neutron scattering measurements have revealed prominent AF correlations with both universal and material-specific features. HgBa₂CuO_4+δ (Hg1201) exhibits a simple-tetragonal structure and thus is free of many of the structural complications of other cuprates. Prior neutron scattering measurements of moderately underdoped Hg1201 revealed a "wineglass"-shaped normal-state AF response [1,2], in contrast to the "hourglass" response seen in other cuprates. Here I will present new results for Hg1201 at even lower doping, near the edge of the SC dome, and discuss the overall doping- and temperature-dependence of the AF response. I will also discuss the relation of this spectrum to prominent energy scales in the cuprates as measured by other probes.