X-ray and neutron diffuse scattering measurements of the local structure of cuprate superconductors*

Nanoscale inhomogeneity is a well-known feature of the cuprate high-temperature superconductors, and recent theoretical and experimental developments have generated renewed interest in the effects of inhomogeneity and local structural distortions on the electronic physics of these materials. We used X-ray and neutron diffuse scattering measurements to study the local structure of several cuprate superconductors, with a focus on the model compound HgBa₂CuO_4+δ which has a small unit cell, simple-tetragonal symmetry at all temperatures, and a high superconducting T_c at optimal doping. Dedicated inelastic neutron scattering measurements were also used to confirm the distinction between static distortions and low-energy fluctuations. We developed structural models guided by 3D-∆PDF analysis of the scattering data in order to understand the local structure of HgBa₂CuO_4+δ. Based on the X-ray and neutron scattering data combined with the modelling results, we discuss the temperature- and doping-dependence of the local structure of HgBa₂CuO_4+δ, the effects it may have on the electronic physics, and the implications for other cuprate materials.