New insight into high-Tc cuprates offered by photon scattering

High-Tc cuprate superconductors are well-known for their antiferromagnetism inherited from the Mott-insulating parent compounds. Visible (Raman) and invisible (X-ray) photon scattering experiments, in particular those that utilize resonant enhancement, allow us to probe dynamic spin correlations with excellent sensitivity. In this talk, I will present results obtained by applying these combined methods to the first two members of the Hg-family of cuprates, Hg1201 and Hg1212. The central finding may be regarded as a magnon counterpart of the isotope effect in conventional superconductors: We find that the single- and bi-magnon energies undergo significant increases from Hg1201 to Hg1212 that correlate with the rises in the superconducting gap energy and Tc. Together with superconductivity’s feedback on the spin excitations, these results strongly support a magnetic pairing mechanism.