Seminars Archive

Soft X-ray scattering and imaging of density-wave orders in quantum solids

Abstract
Strongly-correlated electron systems with competing collective electronic phases are often inherently granular. The spatial organization of the electronic degrees of freedom is essential to understand the phenomenology of these complex systems, yet there are currently no probes of the charge, spin, and orbital degrees of freedom that can simultaneously afford momentum-space sensitivity and nanoscale spatial resolution. In this talk, I will show recent resonant soft X-ray scattering and imaging studies of the spatial textures of electronic orders (charge/spin-density-waves) in cuprate high-Tcs and rare earth nickelate thin films. For the cuprates, I will start by discussing the recent progress on the discovery and characterization of universal charge-density-wave phases in cuprates. I will then present our latest studies of a doping-induced transition from a 'Wigner glass' to a 'Wigner crystal' state in electron-doped Nd2CuO4, occurring around the characteristic doping of the Fermi surface reconstruction (~10%). For the nickelate part, I will discuss recent studies of thin films of NdNiO3, with a focus on scanning resonant magnetic nanodiffraction (<100 nm resolution) experiments to elucidate the spatial organization of spin-density-wave domains as a function of temperature across the Neel transition. I will report observations of domain pinning and return-point-memory effects in the magnetic domain structure, and, most intriguingly, the presence of intrinsic scale-invariant textures with power-law correlations that suggest proximity to a magnetic critical point in this material. I will conclude with some perspectives and a glimpse to very recent resonant coherent diffractive imaging experiments performed at latest-generation, highly-coherent synchrotron X-ray sources to resolve the complex (amplitude/phase) density-wave order parameter down to sub-100 nm resolution.