Seminar 22 July 2015: Dr. Alessandro Ricci, "Critical dynamics and inhomogeneity in complex materials"

The Seminar wil be held on Wednesday 22 July 2015, room "Sergej Tchoudinov"  at 17:00, Physics Division building.

 

Critical dynamics and inhomogeneity in

complex materials

 

Alessandro Ricci

Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg, Germany

alessandro.ricci@desy.de

 

Functional materials like high temperature superconductors (HTS) and complex oxides are characterized by an intrinsic complexity. Indeed, they show the coexistence of multiple striped orders like Charge-Density-Wave (CDW), Spin-Density-Wave (SDW) and defects that get organized in different striped nano-domains and exhibit a strong dynamic competition. The study of the interplay among these multiple orders is challenging because their critical dynamics are strongly connected to the emerging of functional properties at the macroscopic scale. The first step to understand the competition between these multiple striped orders is the investigation of their spatial-organization. On this purpose we developed a set of innovative techniques like scanning micro X-ray diffraction (µXRD) and resonant scanning micro X-ray diffraction (RµXRD) to directly visualize the spatial-organization of the SDW, CDW and defects nano-domains. By the use of µXRD on several High temperature superconductors (HTS) we evidenced a common nanoscale phase separation scenario, characterized by the coexistence of competing scale-free networks of self-organized nano-domains promoting superconductivity [1-8]. Moreover, we found that an optimum inhomogeneity is needed to promote the percolation process and the emergence of properties like superconductivity at the macroscopic scale [9]. In this process, the way how the nano-domains interact and evolve in time is still fundamental missing information. The formation of the striped nano-domains and their domain-wall fluctuations occur at two different time-scales ranging from picosecond up to several seconds. To study both processes we developed new experimental approaches that combine temporal and spatial resolution with bulk sensitivity like resonant IR-pump FEL-probe [10] and time-resolved X-ray Photon Correlation Spectroscopy (XPCS) [11]. Indeed, the developing of the new coherent x-ray sources like Free Electron Lasers or resolution limit Synchrotron Facilities will allow the investigation of otherwise inaccessible phenomena opening the way to the development of new functional materials.

 

  1. G. Campi … and A. Ricci, submitted to Nature (2015)

  2. Drees, Y.*, Z. W. Li*, A. Ricci*, et al., Nature Communications 5, 5731+ (2014). (*these authors equally contribute)

  3. A. Ricci, et al., New Journal of Physics 16, 053030+ (2014).

  4. A. Ricci, et al., Scientific Reports 3, 2383+ (2013).

  5. N. Poccia, M. Fratini, A. Ricci, et al., Nature Materials, 10, 733-736 ( 2011).

  6. A. Ricci, et al., Physical Review B 84, 060511+ (2011).

  7. A. Ricci, et al. Physical Review B 91.2 020503 (2015).

  8. M. Fratini, N. Poccia, A. Ricci, et al., Nature 466, 841 (2010).

  9. N. Poccia, A. Ricci, et al., Proceedings of the National Academy of Sciences 109, 15685 (2012).

  10. A. Ricci, et al., LCLS and FERMI proposals

  11. A. Ricci, Journal of Superconductivity and Novel Magnetism 1-4 (2014).